Download GRG333C Severe and Unusual Weather Supplemental Reference

GRG333C
Severe and Unusual Weather
Supplemental Reference Material
Fall 2015
Troy M. Kimmel, Jr.
Senior Lecturer, Studies in Weather and Climate
Department of Geography and the Environment
University of Texas at Austin
file:
GRG333C.SuppReading.xx.xxxx
GRG333C - Fall 2015
Supplemental Reference Material
Table of Contents
Section
Page(s)
U.S. METAR/SPECI (Surface Aviation Observation) Decode
Surface and Upper Air Station Models
Upper Air (Constant Height) Charts - What They Tell Us
Moisture Terms
Cloud Identification
Forms of Precipitation
Cloud Type Codes and Abbreviations
Precipitation Types and Atmospheric Thermal Structure
A Basic Primer on Weather Forecasting
Surface Air Mass Boundaries: Fronts and Dry Lines
The Spectrum of Low Pressure Types
Heavy Rains in Texas from Pacific Land Falling Tropical Cyclones
Thermodynamic Diagrams - A Basic Primer
NWS WSR88D Doppler Radar Volume Coverage Pattern Descriptions
Convergence / Confluence / Difluence / Divergence - What Does It Mean?
Vorticity Basics
Wind Shear and Thunderstorm Type
A Basic Primer on Thunderstorms
The Thunderstorm Spectrum
A Basic Primer on Severe / Inclement Weather Hazards
Reporting Hail Sizes
A Basic Primer on Tornadoes
Tornadoes, Landspouts, Gustnadoes, Waterspouts,
Funnel Clouds and Wall Clouds... How Do You Tell Them Apart?
Case Study / Tupelo MS EF-3 Tornado - Tues / 28 April 2015
A Basic Primer on Tropical Cyclones
Saffir Simpson Hurricane Wind Scale
Varieties of Drought
Classifications (Degree) of Drought
Weather Safety Rules
Koppen Climate Classification
Weathergraph (Observation and Plotting) - Courtesy: Tim Vasquez
Weathergraph (Forecasting) - Courtesy: Tim Vasquez
1-2
3
4
5
6-7
8-9
10
11
12
13-15
16
17
18
19-21
22
23
24-25
26
27
28
29
30-31
32
33-34
35
36-37
38
39
40
41
42
43
U.S. METAR/SPECI CODE FORMAT WITH REMARKS
METAR/SPECI_ CCCC_ YYGGggZ_AUTO_COR_dddff(f)Gfmfm(fm)KT_dndndnVdxdxdx_VVVVVSM_[RDRDR/VRVRVRVRFT or
RDRDR/VnVnVnVnVVxVxVxVxFT]_w'w'_[NsNsNshshshs or VVhshshs or SKC/CLR]_T'T'/T'dT'd_APHPHPHPH_RMK_(Automated, Manual,
Plain Language)_(Additive and Automated Maintenance Data)
Body of Report: PARAMETER
DESCRIPTION
Type of Report (METAR/SPECI)
METAR is the routine (scheduled) report. SPECI is the non-routine (unscheduled) weather report.
Station Identifier (CCCC)
ICAO station identifier. Consists of four alphabetic characters, e.g., KABC.
Date/Time (YYGGggZ)
Day of the month, followed by the actual time of the report or when the criteria for a SPECI is met or noted.
Group ends with Z to indicate use of UTC. For example, 251456Z.
Report Modifier (AUTO or COR))
AUTO indicates a fully automated report. No human intervention. COR indicates a correction to a previously
disseminated report.
Wind (dddff(f)Gfmfm(fm)KT) (dndndnVdxdxdx)
True wind direction in tens of degrees using three digits. Speed is reported in whole knots (two or three digits).
Gusts (G) are appended to the speed if required. Group ends with KT to indicate knots. For example,
23018G26KT. If wind direction varies by 60° or more and speed is > 6 knots a variable wind group is also
reported, e.g., 180V250. Direction may be reported VRB (variable) if speed is ≤ 6 knots, e.g., VRB05KT. Calm
winds are reported 00000KT.
Visibility (VVVVVSM)
Surface visibility reported in statute miles. A space divides whole miles and fractions. Group ends with SM to
indicate statute miles. For example, 1 1/2SM. Auto only: M prefixed to value < 1/4 mile, e.g., M1/4SM.
Runway Visual Range (RDRDR/VRVRVRVRFT
or RDRDR/VnVnVnVnVVxVxVxVxFT)
10-Minute RVR value: Reported in hundreds of feet if visibility is ≤ one statute mile or RVR is ≤ 6000 feet.
Group ends with FT to indicate feet. For example, R06L/2000FT. The RVR value is prefixed with either M or P
to indicate the value is lower or higher than the RVR reportable values, e.g., R06L/P6000FT. If the RVR is
variable during the 10-minute evaluation period, the variability is reported, e.g., R06L/2000V4000FT.
Present Weather (w'w')
Present weather (other than obscurations) occurring at the station are reported in the body of the METAR/SPECI.
Obscurations are reported if visibility < 7 miles. VA may be reported with any visibility. BCFG and PRFG may
also be reported if visibility ≥ 7SM. Some present weather and qualifiers may be reported if In-the-Vicinity (not at
point-of-observation), e.g., TS, FG, SH, PO, BLDU, BLSA, BLSN, SS and DS. Weather is reported in order of
decreasing dominance. Maximum of three groups reported (precipitation included in one group; separate groups
for other weather). Automated stations can only report RA, SN, UP, FG, BR, FZFG, HZ, and SQ without
augmentation. See table on reverse for more information on qualifiers and weather phenomena.
Sky Condition (NsNsNshshshs or VVhshshs or
SKC/CLR)
Automated stations truncate to three layers up to 12000 feet; if no layers are detected CLR is reported. At manual
stations up to six layers can be reported; if no layers observed SKC is reported. Each layer contains the amount
(FEW, SCT, BKN, OVC) immediately followed by the height using three digits, e.g., FEW015 BKN030. Any
layer containing CB or TCU (manual only) the contraction is appended to the layer height, e.g., FEW015TCU. All
layers are considered opaque. Vertical visibility (VV) is reported in hundreds of feet for an indefinite ceiling, e.g.,
VV002. Surface obscuration (manual only) reported using amount (FEW, SCT, BKN), followed by "000," e.g.,
SCT000; remark required.
Temperature/Dew Point (T'T'/T'dT'd)
Temperature and dew point are reported to the nearest whole degree Celsius using two digits, e.g., 17/13. Sub-zero
values are prefixed with an M, e.g., 03/M02.
Altimeter (APHPHPHPH)
Altimeter is prefixed with an A indicating altimeter in inches of mercury. Reported using four digits; tens, units,
tenths, and hundredths of inches of mercury, e.g., A2990.
Remarks (RMK) -- Divided into two categories: 1. Automated, Manual (Augmented), Plain Language (Manual Only), 2. Additive and Automated Maintenance Data.
The following describes the order in which remarks are reported.
Automated, Manual, Plain Language
Volcanic Eruption, Tornadic Activity (B/E_(hh)mm_LOC/DIR_(MOV), Type of Automated Station (AO1,
AO2), Peak Wind (PK_WND_dddff(f)/(hh)mm), Wind Shift (WSHFT_(hh)mm_FROPA), Tower Visibility
(TWR_VIS_vvvvv), Surface Visibility (SFC_VIS_vvvvv), Variable Prevailing Visibility
(VIS_vnvnvnvnvnVvxvxvxvxvx), Sector Visibility (VIS_[DIR]_vvvvv), Visibility at 2nd Location
(VIS_vvvvv_[LOC], Lightning ([FREQ]_LTG[type]_[LOC]), Begin/End Pcpn (w'w'B(hh)mmE(hh)mm),
Begin/End Thunderstorm (TSB(hh)mmE(hh)mm), Thunderstorm Location (TS_LOC_(MOV_DIR)), Hailstone
Size (GR_[size]), Virga (VIRGA_(DIR)), Variable Ceiling Height (CIG_hnhnhnVhxhxhx), Obscurations
(w'w'_[NsNsNs](hshshs), Variable Sky Condition (NsNsNs(hshshs)_V_NsNsNs), Significant Cloud Types, Ceiling
Height at 2nd Location (CIG_hhh_[LOC], Pressure Rising/Falling Rapidly (PRESRR, PRESFR), Sea-Level
Pressure (SLPppp or SLPNO), Aircraft Mishap (ACFT MSHP), No SPECI ReportsTaken (NOSPECI), Snow
Increasing Rapidly (SNINCR_[inches-hr/inches on ground]), Other Significant Information (agency specific, e.g.,
LAST)
Additive and Automated Maintenance Data
Hourly Precipitation Amount (Prrrr), 3- and 6-Hour Precipitation Amount (6RRRR), 24-Hour Precipitation
Amount (7R24R24R24R24), Snow Depth on the Ground (4/sss), Water Equivalent of Snow on Ground (933RRR),
Cloud Types (8/CLCMCH), Duration of Sunshine (98mmm), Hourly Temperature and Dew point: 0.1°C
(TsnT'T'T'snT'dT'dT'd), 6-Hour Maximum Temperature: 0.1°C (1snTxTxTx), 6-Hour Minimum Temperature: 0.1°C
(2snTnTnTn), 24-Hour Maximum/Minimum Temperature: 0.1°C (4snTxTxTxsnTnTnTn), 3-Hour Pressure Tendency
(5appp), Sensor Status Indicators: RVRNO, PWINO, PNO, FZRANO, TSNO, VISNO_LOC, CHINO_LOC,
Maintenance Check Indicator: $
If an element or phenomena does not occur, is missing, or cannot be observed, the corresponding group and space are omitted (body and/or remarks) from that particular report, except for Sea-Level Pressure (SLPppp), and
3-, 6-, and 24-Hour precipitation groups. At designated stations, SLPNO shall be reported in a METAR when the SLP is not available.
U.S. DEPARTMENT OF COMMERCE
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
National Weather Service - Observing Systems Branch
1325 East-West Highway
Silver Spring, MD 20910
METAR\TA1\2-8-96
1
NOTATIONS FOR REPORTING WEATHER PHENOMENA
QUALIFIER
Intensity or Proximity
Light
VC
no sign
Moderate
+
Heavy
In the Vicinity
Descriptor
MI
Shallow
PR
Partial
BC
Patches
DR
Low Drifting
BL
Blowing
SH
Shower(s)
TS
Thunderstorm
FZ
Freezing
RA
Rain
WEATHER PHENOMENA
Precipitation
DZ
Drizzle
IC
Ice Crystals
UP
Ice Pellets
PE
Unknown Precipitation (auto; no intensity)
SN
Snow
SG
Snow Grains
GR
Hail
GS
Small Hail/Snow Pellets
Obscuration
BR
Mist
FG
Fog
FU
Smoke
VA
Volcanic Ash
DU
Widespread Dust
SA
Sand
HZ
Haze
PY
Spray
SQ
Squalls
FC
Funnel Cloud(s)
(Tornado, or Waterspout)
SS
Sandstorm
Other
PO
Well Developed
Dust/Sand Whirls
DS
Duststorm
REPORTING OF LAYERS
AUTOMATED STATIONS
REPORTABLE CONTRACTIONS FOR SKY COVER
Reportable Contraction
Meaning
Summation Amount of Layer
Priority
VV
Vertical Visibility
8/8
1
lowest few layer
SKC or CLR
Clear
0
2
lowest broken layer
FEW
Few
<1/8 - 2/8
3
overcast layer
SCT
Scattered
3/8 - 4/8
4
lowest scattered layer
BKN
Broken
5/8 - 7/8
5
second lowest scattered layer
OVC
Overcast
8/8
6
second lowest broken layer
SKC is reported at manual stations when no clouds are observed.
CLR is reported at automated stations when no clouds are detected at or below 12000 feet.
REPORTABLE VISIBILITY VALUES -- Automated
M1/4, 1/4, 1/2, 3/4, 1, 1 1/4, 1 1/2, 1 3/4, 2, 2 1/2, 3, 4, 5, 6, 7, 8, 9, 10
Layer Description
7
highest broken layer
8
highest scattered layer
REPORTABLE VISIBILITY VALUES -- Manual
0, 1/16, 1/8, 3/16, 1/4, 5/16, 3/8, 1/2, 5/8, 3/4, 7/8, 1, 1 1/8, 1 1/4, 1 3/8,
1 7/8, 2, 2 1/4, 2 1/2, 2 3/4, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 20, 25, 30, 35,
40, etc., in 5 mile increments.
FORMAT AND ORDER OF CODED REMARKS -- Times of Transmission
Synoptic Cloud Types, 8/CLCMCH (manual)
00
03
06
09
12
15
18
21
X
X
X
X
X
X
X
X
Snow Increasing Rapidly, SNINCR [inches/hr]/[inches on ground] (manual)
Hourly
X1
Depth of Snow on the Ground, 4/sss (manual)
X2
X1
X2
Water Equivalent of Snow on the Ground, 933RRR (manual)
X
Duration of Sunshine, 98mmm (manual)
0800 UTC
Hourly Precipitation Amount, Prrrr (automated stations only)
Hourly
X3
3- and 6-Hour Precipitation Amount, 6RRRR
X4
X3
X4
24-Hour Precipitation Amount, 7R24R24R24R24
X4
X3
Hourly
6-Hour Maximum Temperature, 1snTxTxTx
X
X
X
X
6-Hour Minimum Temperature, 2snTnTnTn
X
X
X
X
24-Hour Maximum/Minimum Temperature, 4snTxTxTxsnTnTnTn
Midnight Local Standard Time (LST)
Pressure Tendency, 5appp
-
X4
X
Hourly Temperature and Dew Point, TsnTaTaTasnT'aT'aT'a
1
2
3
4
X3
X
X
X
included whenever there is more than a trace of snow on the ground
included whenever there is more than a trace of snow on the ground and more than a trace of precipitation occurred within the past 6 hours
6-hour precipitation amount
3-hour precipitation amount
2
X
X
X
X
X
GRG333C / Severe and Unusual Weather
Surface and Upper Air Station Models
200M B :
(Appx 39,000'
M SL)
-57C / Air Tem perature
4C Dew Point Depression
(-61C / Dew Point Tem perature)
W ind: 250 Degrees / 110 Knots
Pressure Height (Prefix 1,Suffix 0):
12130 Meters
12 Hour Height Change:
+ 20 Meters
Center Circle: Blackened - Dew Point Depression is 5C or Less
250M B:
(Appx 34,000'
M SL)
-45C / Air Tem perature
4C Dew Point Depression
(-49C / Dew Point Tem perature)
W ind: 250 Degrees / 110 Knots)
Pressure Height (Prefix 1, Suffix 0):
10670 Meters
12 Hour Height Change:
+ 10 Meters
Center Circle: Blackened - Dew Point Depression is 5C or Less
300M B:
(Appx 30,000'
M SL)
-37C / Air Tem perature
1C Dew Point Depression
(-38C / Dew Point Tem perature)
W ind: 250 Degrees / 100 Knots
Pressure Height (Suffix 0):
9440 Meters
12 Hour Height Change:
+ 20 Meters
Center Circle: Blackened - Dew Point Depression is 5C or Less
500M B:
(Appx 18,500'
M SL)
-14C / Air Tem perature
27C Dew Point Depression
(-41C / Dew Point Tem perature)
W ind: 250 Degrees / 55 Knots)
Pressure Height (Suffix 0)
5720 Meters
12 Hour Height Change:
- 10 Meters
Center Circle: Not Filled - Dew Point Depression is > 5C
700M B:
(Appx 9,600'
M SL)
1C / Air Tem perature
23C Dew Point Depression
(-22C / Dew Point Tem perature)
W ind: 270 Degrees / 25 Knots
Pressure Height (Prefix 2 or 3)
3097 Meters
12 Hour Height Change:
+ 20 Meters
Center Circle: Not Filled - Dew Point Depression is > 5C
850M B:
(Appx 4,600'
M SL)
6C / Air Tem perature
12C Dew Point Depression
(-6C / Dew Point Tem perature)
W ind: 010 Degrees / 10 Knots
Pressure Height (Prefix 1)
1525 Meters
12 Hour Height Change
+20 Meters
Center Circle: Not Filled - Dew Point Depression is > 5C
CONSTANT HEIGHT CHART NOTE (FOR STATION M ODELS ABOVE):
“x” in the Dew Point Depression Position Indicates Dew Point Depression of > 29C
Dew Point Depression is Not Plotted on Som e Constant Height Charts W hen Air Tem perature is < -41C
SURFACE:
77F / Air Tem perature
5 Miles Visibility / Rain Shower
71F / Dew Point Tem perature
Center Circle: Cloud Coverage
Cloud Types / Bases
GRG333CSurfaceUpperAirStationModels.wpd
3
Surface Pressure
(Add Decim al Point Before Last #,
Prefix with 9 or 10 to Bring W hole
Num ber Closest to 1000.0)
999.8 Millibars
3 Hour Pressure Change/Tendency
-0.3 Millibars
GRG333C / Severe and Unusual Weather
Constant Height (Upper Air) Charts - What They Tell Us
850 MB Constant Height (Upper Air) Chart - Approximately 4,600 ASL
(Constant Height Contours Drawn Every 30 Meters)
Strongly affected by heating and cooling of Earth.
Represents near surface conditions although this is not considered to be in the boundary/friction layer which is only found up to 2,000
to 3,000 feet AGL (more during the heating of the day).
Low level moisture: Watch for relative humidities above 60% (to be drawn in green)
Warm / Cold air advection: Watch for height contours being perpendicular to isotherms (indicating advection)
Fronts: Watch for frontal boundaries at 850 mb
Forecast tools:
(1) In summer, take 850 mb temperature overhead and add 15 C / 27 F to approximate day’s high
(2) In winter, take 850 mb temperature overhead and add 9 C / 16 F to approximate day’s high
(3) In winter, 850 mb temperature overhead must be 0 C or lower for precipitation to transition
from liquid to frozen
700 MB Constant Height (Upper Air) Chart - Approximately 9,600 ASL
(Constant Height Contours Drawn Every 30 Meters)
Mid Level Dry Air Intrusion at this level in severe thunderstorm situations
Air Mass (Single Cell) thunderstorms are steered by winds at this level
Thunderstorm Development: When air temperature at 700 mb is 14 degrees C / 57 degrees F or higher, this tends to preclude
thunderstorm development (indicating a lid or “inversion” in the atmosphere; warmer air aloft)
500 MB Constant Height (Upper Air) Chart - Approximately 18,500 feet ASL
(Constant Height Contours Drawn Every 60 Meters)
One half (1/2) the mass or weight of the Earth’s atmosphere is located below/above this spot (considering that the average (or
standard) atmospheric pressure is 1013.2 millibars at the surface.
Find troughs and ridges (leading to convergence and divergence in our middle and upper atmosphere)
Surface weather systems are steered by 500 mb directional flow but at only 1/4 to 1/2 of the wind speed found
at 500 mb.
300 MB / 200 MB Constant Height (Upper Air) Charts 300 MB Approximately 30,000 feet ASL, 200 MB Approximately 39,000 feet ASL
(Constant Height Conrours Drawn Every 120 Meters)
Good for detecting: upper air divergence / upper air convergence, jet stream s (polar jet stream s around 30,000 ASL,
subtropical jet stream s around 35,000 to 40,000 feet), jet streaks. Isotachs are plotted to denote jet stream s/jet streaks.
Directional / Speed Divergence aloft is favorable for surface convergence below and for cyclogenesis
Stronger winds aloft help to ventilate developing thunderstorm s so that continue to strengthen and becom e supercells;
also it assists in causing a slight tilt in the cum ulonim bus tower in order to keep the updraft and downdraft of a strom
separate m aking it longer lasting.
4
MOISTURE TERMS
Air Temperature – The measured “hotness” or “coldness” of the parcel of air being
sampled.
Dew Point Temperature – The temperature to which you would have to cool the air to,
given a constant pressure and moisture content, in order for air in the parcel to become
saturated.
Relative Humidity – Expressed as a percentage, the ratio of the air’s actual moisture
content compared to how much moisture could coexist in the air at that given air
temperature. Relative humidity is temperature dependent. Relative humidity does not tell
you how much moisture in present in the atmosphere; it only tells you how close you are to
saturation.
Relative humidity = (vapor pressure / saturation vapor pressure) x 100%
Vapor Pressure – The atmospheric pressure contributed by water vapor in our
atmosphere. Vapor pressure states the absolute amount of water vapor in our atmosphere.
Vapor pressure -- or the pressure exerted by water vapor -- in our atmosphere ranges from
near 0 millibars (mb) in colder, drier climates to as much as 60 millibars (mb) in moist
tropical environments.
Saturation Vapor Pressure (also referred to as Equilibrium Vapor Pressure) – The vapor
pressure at which the air becomes saturated. Saturation vapor pressure is solely
temperature dependent; it is much higher in higher temperatures. The atmosphere contains
over 80 times as much moisture at 86 degrees F/30 degrees C as it does at -22 degrees F/
-30 degrees C.
Mixing Ratio – W ithin a parcel of air, the ratio of the mass (or weight) of water vapor per
volume of air compared to the remaining mass (or weight) of dry air.
Mixing Ratio = within an air parcel, mass of water vapor (grams) / mass of dry air
(kilograms)
Absolute Humidity – The mass (or weight) of water vapor per volume of air, usually
expressed as grams of water vapor per cubic meter of air. Absolute humidity changes as
air pressure changes.
Absolute Humidity = mass of water vapor in air (grams) / volume of air (cubic meters)
Specific Humidity – The ratio of the mass (or weight) of water vapor in a parcel of air
compared to the total mass (or weight) of the parcel of air, including the water vapor.
5
CLOUD IDENTIFICATION
(MODIFIED; AFTER MOGIL/LEVINE)
High Clouds (At or Above 20,000 feet)
-Cirrus (Ci) Wispy streamers, waves or masses of mostly ice crystal (some
supercooled water droplets) clouds usually at heights of 20,000 feet or
more. Fair weather unless they thicken into altostratus (As). Referred to
as "mares tales." Usually west to east with upper level (jet stream) wind.
-Cirrocumulus (Cc) Very small cumulus puffs, usually smaller then size of
end of thumb when held at arms length, at the cirrus level. Has rippled
appearance and can occur individually or in long rows often covering only
portions of the sky. These clouds can indicate instability at upper levels
of the atmosphere. Referred to as "mackerel sky," since rippled appearance
often resembles scales of fish.
-Cirrostratus (Cs) A stratified (thin sheet like) layer of white cirrus
clouds that often covers the entire sky. So thin that the sun and moon can
be clearly seen through with "halo" effect (usually transparent to
sunlight). Shadows are cast. Fair weather clouds unless they thicken into
altostratus.
Middle Clouds (6,500 to 20,000 feet)
-Altocumulus (Ac) Gray, puffy, rounded masses of cumulus clouds with bases
between 8,000 and 12,000 feet. Sometimes rolled out in parallel waves or
bands with bases darker than other parts of the same cloud. Individual
cumulus puffs should be about the size of the ball of your thumb when your
hand is held at arms length. Referred to "rising castles" (called
castellanus) indicate instability at mid levels of the atmosphere.
-Altostratus (As) Gray to blue gray (never white) cloud usually covering
the entire sky. Bases are between 8,000 and 12,000 feet. Sun may appear as
a dull rounded disk with no shadows cast. Usually form in advance of storms
that produce much widespread and continuous precipitation.
Low Clouds (Surface to 6,500 feet)
-Stratus (St) A uniform grey stratified layer of low clouds within 2,000
feet of the ground. Can cover portions of or the entire sky. Only light
drizzle or light snow grains fall from true stratus clouds. Fog occurs when
stratus clouds are in touch with the ground surface. Very uniform cloud
bases.
-Stratocumulus (Sc) Low, lumpy cloud layer with bases from 3,000 to 5,000
feet. These clouds contain more water and the cumulus puffs are larger than
altocumulus. Appears in rows, patches or in rounded masses with blue sky
visible between cloud elements. Sometimes occurs with the spreading out of
cumulus clouds later in the day. Color ranges from white to dark gray.
Little or no precipitation expected. To distinguish from altocumulus, hold
your hand at arm's length. Stratocumulus cloud elements will be larger than
the size of the ball of your thumb up to about the size of your balled
fist.
6
-Nimbostratus (Ns) A dark, gray wet-looking cloud characterized by more or
less continuously falling precipitation (rain or snow) of light or moderate
intensity (never heavy precipitation). It is not characterized by thunder,
lightning or hail. Bases of nimbostratus is normally impossible to identify
clearly (because of precipitation). No sun or moon visible through cloud
mass.
Clouds of Vertical Extent
-Cumulus (Cu) A cloud in the form of individual, detached domes or towers
that are usually quite dense and well defined. Characterized by flat bases
with bulging cauliform like upper part. Generally fair weather clouds that
look like cotton puffs. These clouds indicate rising air motions
(convection). Bases are generally 5,000 feet or below. (Cumulus Humilis)
-Cumulus clouds when appearing as small and broken fragments with a ragged
edge are referred to as "cumulus fractus."
-Moderate Cumulus (Cumulus Congestus)
-Towering Cumulus (Cumulus Congestus)
-Building Cumulus (Cumulus Congestus)
-Cumulonimbus (Cb) Large, towering (precipitating) cumulus clouds
accompanied by thunder, lightning and rain. Bases generally between 2,000
(tropical environments) and 10,000 feet (more arid environments); tops as
high as 60,000 to 70,000 feet in more severe storms. Cirrus clouds, at top
of parent cumulonimbus cloud, can be carried hundreds of miles away from
the parent cloud by upper level winds near the tropopause. From a distance,
the top of the cumulonimbus may look like a blacksmith's anvil.
Cloud Subtypes / Variations
Cloud subtype
Latin Meaning...
Associated with...
Lenticularis
Fractus
Humilis
Congestus
Undulatus
Translucidus
Mammatus
Pileus
Castellanus
Lens like
Broken or Fractured
Of small size
To pile up; become congested
Having waves
To shine through
Bag/pouch like; Mammary
Cap
Small castles
Ac
St, Cu, Ns
Cu
Cu
Ac
Cs
Cb
Ac
Ac
Contrails
Condensation trails
7
FORMS OF PRECIPITATION
(AMS GLOSSARY OF METEOROLOGY)
Drizzle
Very small, numerous, and uniformly dispersed water drops that appear to
float while following air currents. Unlike cloud/fog droplets, drizzle
actually falls to the ground. It usually falls from low stratus clouds and
is frequently accompanied by low visibility and fog. By convention, drizzle
drops are considered to be less than 0.5 millimeter/0.02 inch.
Intensity of drizzle is based upon rate of fall:
(a) "very light" is when exposed surface is never completely wet
(b) "light" is when rate of fall is trace to .01" per hour
(c) "moderate" is when rate of fall being .01" to .02" per hour
(d) "heavy" is when rate of fall is more than .02" per hour even though
when rate is equal or exceeds .04" per hour, all or part of the
precipitation is generally rain
Rain
Precipitation in the form of liquid water drops, which have diameters
greater than 0.5 millimeter/0.02 inch, or, if widely scattered, the drops
may be smaller. Generally produced by nimbostratus or cumulonimbus clouds.
Intensity is classified as:
(a) "very light" when scattered drops do not completely wet an exposed
surface regardless of duration
(b) "light" when the rate of fall varies between a trace and .10" per hour
with the maximum rate of fall being no more than .01" in six minutes
(c) "moderate" when the rate of fall is between .11" and .30" per hour with
the maximum rate of fall being no more than .03" in six minutes
(d) "heavy" with over .30" per hour or more than .03" in six minutes.
Freezing Rain
Rain (see above) that falls in liquid form but freezes upon impact to form
a coating of glaze on the ground and exposed objects. When the temperature
of the ground surface and glazed objects initially must be near or below
freezing, it is necessary that the water drops be supercooled before
striking. Freezing rain frequently occurs as a transient condition between
the occurrence of rain and ice pellets (sleet). When encountered by an
aircraft in flight, freezing rain can cause a dangerous accretion of clear
aircraft icing. Droplet size, as in rain, must be greater than 0.5
millimeter/0.02 inch.
Freezing Drizzle
Drizzle (see above) that falls in liquid form but freezes upon impact to
form a coating of glaze. The physical cause of this phenomena is the same
as that for freezing rain (see above). Droplet size, as in drizzle, must be
less than 0.5 millimeter/0.02 inch.
8
Ice Pellets (Sleet)
A type of cold weather precipitation consisting of transparent or
translucent pellets of ice, 5 millimeters/0.2 inch or less in diameter.
They form from the freezing of rain droplets or refreezing of largely
melted snowflakes when falling through a below-freezing layer of air near
the earth's surface. The ice pellets may be spherical, irregular, or
(rarely) conical in shape. Ice pellets usually bounce when hitting the
ground and usually make a distinctive sound.
Snow
Cold weather precipitation form composed of white or translucent ice
crystals, chiefly in complex branched hexagonal form and often agglomerated
into snowflakes. Snow is produced in supercooled clouds where water vapor
is deposited (deposition) as ice crystals that remain frozen during their
entire descent. Snowflakes can be up to 2 millimeters/0.8 inch in diameter.
Intensity of snow is based upon visibility:
(a) "light" snow is when visibility is 5/8 statute mile or more
(b) "moderate" snow is when visibility is less than 5/8 but more than 5/16
statute mile
(c) "heavy" snow is when visibility is less than 5/16 statute mile
Hail
Precipitation in the form of balls or irregular lumps of ice, always
produced by convective clouds (cumulonimbus). By convention, hail has a
diameter of 5 millimeters/0.2 inch or more, while smaller particles of
similar origin may be classified as ice pellets or snow pellets (graupel).
Thunderstorms which are characterized by strong updrafts, large liquid
water contents, large cloud droplet size and great vertical heights are
favorable to hail formation. Hail size is important in determining the
strength, of course, of the up and downdrafts and, therefore, the severity
of thunderstorms. By definition, hail size of 1.00 inch (1 inch) or greater
is one criteria that classifies a thunderstorm as being "severe."
9
CLOUD TYPE CODES AND ABBREVIATIONS
High Clouds
Middle Clouds
Low Clouds
10
11
12
Surface Air Mass Boundaries:
Fronts and Dry Lines
A Basic Primer
Prepared by Troy Kimmel
Senior Lecturer, Studies in W eather and Climate
Department of Geography and the Environment
University of Texas at Austin
Surface boundaries between air masses are almost always marked by the presence of a front and a trough of
lower pressure or by the presence of the dry line. These boundaries, if moving, and if moving into an air mass
with sufficient atmospheric moisture and instability, can be marked by clouds and precipitation due to the
atmospheric lift accompanying the feature. If moving little or not moving at all, these systems may have little
associated sensible weather.
The development and forward movement of fronts and dry lines as well as the sensible weather that they
produce are heavily influenced by the upper tropospheric wind field. In general, depending on the type of front
present, winds that are stronger and that blow more perpendicular to the frontal boundary will result in a faster
forward movement with upper level winds that are more parallel to the frontal boundary often resulting in a
front having little forward movement. In general, in order for cold, warm and occluded fronts to be labeled as
such, they should have a forward motion of 4 to 5 mph or greater.
As mentioned above, surface frontal boundaries are found within “lines” (or troughs) of low pressure. As the
front approaches your location, the atmospheric pressure will decrease until the time that the front actually
passes; at that time, pressure will begin to rise as the new air mass moves into your area. This pressure
difference is usually most distinct along cold fronts and a little less noticeable along warm, stationary and
occluded fronts. Pressure difference along dry lines is even less apparent which is one of the primary reasons
that dry lines are not considered as a traditional type of front.
COLD FRONTS
A cold front is, due to its steep vertical nature, the most
dynamic type of front. It marks the boundary where colder
air (cP, mP or cA air masses) is actively advancing or
moving into an area formerly occupied by warmer air (mT,
cT or even modified cP or mP air masses). Because of the
steep slope, created as colder, more dense air displaces
the warmer, more moist air to the east upward,
precipitation/thunderstorms are more likely (given moisture
and instability) in a narrow band along the frontal boundary.
A cold front is drawn, on surface weather maps, in blue with
triangles pointing into the direction the front is moving.
13
Page 2
THE WARM FRONT
A warm front marks the boundary where warmer air (mT
or CT air) is actively advancing or moving into an area
formerly occupied by colder air (cP, mP or cA air masses).
Because warmer air doesn’t replace colder air - from the
top down - the same way that colder air replaces warmer
air - from the bottom up, the frontal boundary is much
more gently sloping than the cold front. As a result, cloud
cover tends to cover a much larger area on the cold side
of the warm front with a wide area of lowering clouds, fog
and light precipitation in the area. As the warm front
moves through a given location, winds shift to the south
and skies often partially clear with warmer and more
humid conditions. Even though severe thunderstorms are
not climatologically favored along a warm front (because
of the more gentle slope), they can occur in situations
when upper air winds are strong in speed as well as
strongly divergent. The warm front is drawn, on surface
weather maps, in red with half circles pointing into the
direction the front is moving.
THE STATIONARY FRONT
The stationary front results when upper air patterns weaken and the upper level winds begin blowing more
parallel to the formerly cold or warm front. As a result, the frontal movement slows and the front becomes
“stationary.” A wide variety of weather can be found along stationary fronts all the way from clear skies to
clouds and even precipitation and thunderstorms. This is
often decided by the upper tropospheric wind field and
any disturbances in that parallel (to the front) upper air
wind.
Over Texas, research has shown that flash floods can
occur as a stationary front is in place across the area as
upper air disturbances move overhead causing a
continuous “training” effect of thunderstorms along the
front, which, of course, isn’t moving.
Stationary fronts are drawn in alternating blue and red
segments with blue triangles/red half circles.
14
Page 3
THE OCCLUDED FRONT
The occluded front forms when, in the vicinity of a surface
extratropical cyclone, the eastward moving cold front overruns a
warm front in the eastern or southeastern quadrant of the low
pressure area. This is found most often in the central and northern
parts of the United States into Canada.
The occluded front is drawn in purple with alternating red half
circles and blue triangles pointing into the direction that the front is
moving.
THE DRY LINE
The dry line is a feature generally found in the central and
southern parts of the United States plains states and is the boundary
between dry air (cT air mass from the southwestern USA and
northern Mexico) to the west and moist air (mT air mass from the Gulf
of Mexico) to the east. It can occur anytime spring, summer into the
autumn months, but is most dynamic during the process of surface
cyclogenesis over the plains as west and southwesterly winds on the
southwest side of the extratropical cyclone sweeps dry air east
northeastward out of the southwest USA and northern Mexico.
Because dry air has a higher molecular weight and is more dense
than moist air, the dry line, when moving eastward, can produce
dynamic atmospheric lift. This, in combination with abundant low
level moisture and atmospheric instability ahead of the dry line, can
result in a narrow band of thunderstorms, some severe, in advance of
the eastward moving dry line. In the wake of the dry line, as the air’s
dew point/relative humidity quickly drops, the air temperature is often
much warmer.
If associated with an extratropical (frontal) cyclone, the dry line can
move as far eastward as the eastern plains and western Mississippi
Valley. Absent of an extratropical cyclone, dry lines often move
eastward during the day time hours and then retreat westward at night.
Images Courtesy of:
Thompson - Brooks Cole Higher Learning
John Brandon’s “Fly Safe” Tutorials
WeatherBug / Earth Networks
Wikipedia
Prentiss Hall Publishing
NOAA/NWS, Weather Prediction Center, College Park, MD
WDTN TV Weather, Dayton, OH
The Weather Channel (Weather.Com)
15
Kendall Hunt Publishing
NOAA/NWS, Fort Worth, TX
WJLA TV Weather, Washington, DC
The Spectrum of Low Pressure Types
(Diagram: Beven, NHC, 1997)
Warm
Core
Systems
Tropical
Cyclones (Low)
Extratropical
“Bombs”
Polar Cyclones (Low)
-Strange Hybrids
Monsoon
Depressions
Cold
Core
Systems
Subtropical
Cyclone (Low)
Extratropical
Cyclone (Low)
Non-Frontal
Frontal
Definitions to know....
Tropical cyclone (low): A warm-core non-frontal synoptic-scale cyclone, originating over tropical or
subtropical waters, with organized deep convection and a closed surface wind circulation about a
well-defined center. Once formed, a tropical cyclone is maintained by the extraction of heat energy from the
ocean at high temperature and heat export at the low temperatures of the upper troposphere. In this they
differ from extratropical cyclones, which derive their energy from horizontal temperature contrasts in the
atmosphere (baroclinic effects).
Subtropical cyclone (low): A non-frontal low-pressure system that has characteristics of both tropical and
extratropical cyclones. Like tropical cyclones, they are non-frontal, synoptic-scale cyclones that originate
over tropical or subtropical waters, and have a closed surface wind circulation about a well-defined center. In
addition, they have organized moderate to deep convection, but lack a central dense overcast. Unlike
tropical cyclones, subtropical cyclones derive a significant proportion of their energy from baroclinic sources,
and are generally cold-core in the upper troposphere, often being associated with an upper-level low or
trough. In comparison to tropical cyclones, these systems generally have a radius of maximum winds
occurring relatively far from the center (usually greater than 60 n mi), and generally have a less symmetric
wind field and distribution of convection.
Extratropical cyclone (low): A cyclone of any intensity for which the primary energy source is baroclinic,
that is, results from the temperature contrast between warm and cold air masses (generally associated with
frontal zones).
(Definitions courtesy of NOAA/NWS/National Hurricane Center)
16
Heavy Rains in Texas from Pacific Land Falling Tropical Cyclones...
Are They Really the Result of Pacific Moisture?
Troy Kimmel email to a lead NWS Forecaster in Texas...
“It seems that time to time some WFOs and broadcast mets talk about the abundant tropical moisture that is
coming into Texas from the remnants of land falling Pacific tropical cyclones (west coast of Mexico) and how
ongoing rain or flooding in Texas comes as a result of that Pacific moisture. They seem to conveniently forget
about the scouring effect of low level moisture by the Sierra Madre Occidental and Oriental mountains chains
between here and the landfall position and how they can even scour out even a little lower mid level moisture.
After the scouring effect, in the mid and upper levels, the remnants of the Pacific moisture is, of course, found in
a colder temperature environment (sub freezing above central Texas in general at or above 16,000 ft to 17,000
ft AGL?). So the question becomes, how much water vapor - Pacific or otherwise - can co-exist in that mid and
high level colder temperature environment?
Is there any documentation that has examined soundings in the environment, as outlined above, and how much
water vapor can be attributed back as being Pacific, in systems over our area? Bob Rose, over at the LCRA,
said he thinks he has seen an email or two addressing this and that he remembers that who ever the author
was, has said that, at best, by the time you get into north and central Texas, the most moisture you can attribute
back to the Pacific Ocean moisture in these systems is maybe 10% (if even that).
Am I off base on all of this in thinking that it is often the dynamics of these remnant Pacific systems rather than
all of that "abundant" Pacific moisture that causes our problems in Texas?”
A lead NWS Forecaster in Texas... his response to Troy’s question...
“Your take on the situation is absolutely correct. The notion that moisture of any significant value arrives with a
Pacific cyclone is grossly exaggerated for the sake of simply communicating what is occurring to a public that's
not scientifically savvy. Most of the moisture below 10,000 feet is rung out before it gets here. What is
unfortunate is that the simplified version infects some meteorologists as the primary reason that the rains are
occurring, when it's just not scientifically accurate. I have a couple of times in the past tried to explain the
process in an AFD, but it's difficult to combat the "prevailing" theory in an operational product...hence my desire
for more official research and ultimately publication.
Yes, the upper level dynamics are absolutely more important in these types of flooding events. If you want to
google "Flooding associated with predecessor rain events" (PREs) it will describe the dynamics that occur with
tropical cyclones from the Atlantic Ocean and how they affect the midwest/northeast with flooding events ahead
or in advance of the remnant storm. There's a great powerpoint to view from WPC I believe. The topic I'm
researching is Pacific cyclones affecting Texas with PREs. The difference between the Atlantic/midwest event
and the Pacific/Texas event is that the Gulf of Mexico must be "open" to supply Texas with deep moisture in the
lower levels (to replace what has been lost over the mountains). This is why every Pacific cyclone landfalling in
Mexico doesn't result in flood events here even when the satellite shows the infamous "tropical connection"
streaming over Texas. It's also why in this event, we saw the low center over Arizona and New Mexico
producing a stream of heavy rain from West Texas to Central Texas, all of the way into Southeast Texas...well
in advance of the low. This was a classic Pacific/Texas PRE setup and I'm thankful to have another case to add
to the database.
Having said all of that, the upper level moisture from the tropical cyclone is still essential for flooding events.
The moist air allows for warm-rain and efficient precipitation processes to dominate, and this moisture can't
arrive from just an "open" gulf.
Anyway, I'm headed out for the day, but if there's any other questions, I can go into better detail about what the
synoptic set up tends to look like when we actually do get these PREs here. And for whatever reason, it seems
the Waco to Austin area seems to be region where the heaviest rains from PREs tend to occur.”
(KimCo Met Services) 2014.0921.Pacific Tropical Origin Heavy Tropical Rains in Texas.pdf
17
Thermodynamic Diagrams
A Basic Primer
Prepared by Troy Kimmel
Lecturer, Studies in Weather and Climate
Department of Geography and the Environment
University of Texas at Austin
Thermodynamic diagrams are used to graphically depict upper air data (temperature, humidity, pressure and
wind) with height above ground as gathered by rawinsondes/upper air balloons and atmospheric profilers. You
will also see model forecast data presented in thermodynamic diagram form so be careful to know whether you’re
looking at actual observed or forecast model data. The data presented in a thermodynamic diagram is also
referred to as a “sounding.”
There are several different types of thermodynamic diagrams. We will utilize the “Skew-T” diagram which has the
temperature lines skewed to the right as you go upwards on the diagram (from the bottom axis which depicts the
temperature).
Since rawinsondes/upper air balloons are released only every 12 hours (at 00z and 12z GMT), it is extremely
important to remember that the sounding is only a snapshot of the data as it was back at 00z or 12z GMT.
Atmospheric profilers constantly sense the atmosphere so the sounding data from the profilers is updated much
more frequently.
In reading the chart, across the bottom axis, you’ll see temperature (in C degrees) denoted (with the temperature
lines skewed to the right as you go up as noted above), while the left side of the graphic depicts the height in the
atmosphere. We’ll utilize the constant height surface depictions (850mb, 700mb, etc) to denote height. The row
of numbers to the right of the chart are various derived indices (lifted index, etc) based on the sounding data.
The two solid lines on the chart, as you go up, are air temperature (the right most solid line) and the dew point
temperature (the left most solid line) and the parcel ascent temperature (the dashed line).
Thermodynamic diagrams help the meteorologist diagnose the following atmospheric elements:
M AIR TEMPERATURE: You can evaluate the air temperature (measured in degrees C) from the surface
upwards through the troposphere and into the lower stratosphere
M AIR TEMPERATURE INVERSIONS: You can identify temperature inversions (the “cap”) and through cross
examination with other parameters and weather charts, identify the inversion type (frontal, subsidence)
M MOISTURE: The air’s dew point temperature (measured in degrees C) is depicted on the entire ascent of the
rawinsonde all the way from near the surface through the troposphere showing in what atmospheric layers
moisture is concentrated (remember that just because the atmosphere is saturated doesn’t necessarily mean that
the amount of moisture in the atmosphere is great)
M WIND: Wind speed (measured in knots) and wind direction with height from near the surface through the
troposphere as denoted on the right hand side of the diagram (using standard wind barbs)
M ATMOSPHERIC STABILITY/INSTABILITY: By referencing the position of the parcel ascent temperature line
and comparing it to the environmental air temperature lapse rate, we can determine atmospheric stability (CINH)
and instability (CAPE)
What thermodynamic profiles DON’T tell you (by themselves):
- Presence of clouds or precipitation (although they can tell you the likelihood of clouds and where they are,
heightwise, in the troposphere by indicating where the atmosphere is more saturated)
- Whether there is mechanical lift going on in the atmosphere
18
NATIONAL WEATHER SERVICE
WSR88D / Volume Coverage Pattern (VCP) Descriptions
PRECIPITATION MODES
VCP11 / VCP211 - Convective Weather Mode
Short Pulse - 14 Elevation Scans in 5.0 Minutes
Lowest Scan: 0.5 Degree Elevation / Highest Scan: 19.5 Degree Elevation
In Lowest Levels, Scans at 1.0 Degree Intervals
(Scans at .5 / 1.5 / 2.4 / 3.4 / 4.3 / 5.3 / 6.2 / 7.5 / 8.7 / 10.0 / 12.0 / 14.0 / 16.7 / 19.5 Degrees)
Detection of.. Severe and Non-Severe Convective Weather Phenomena
(May Be Used When Thunderstorms Are Very Near or In The Radar Site’s “Cone of Silence”)
VCP12 / VCP212 - Rapid “Severe” Weather Mode
Short Pulse - 14 Elevation Scans in 4.5 Minutes
Lowest Scan: 0.5 Degree Elevation / Highest Scan: 19.5 Degree Elevation
In Lowest Levels, Scans at 0.5 Degree Intervals Which Allows for More Concentration on
Lower Elevation Scans; Better Resolution
(Scans at .5 / .9 / 1.3 / 1.8 / 2.4 / 3.1 / 4.0 / 5.1 / 6.4 / 8.0 / 10.0 / 12.5 / 15.6 / 19.5 Degrees)
Detection of.. Severe Convective Weather Phenomena (squall lines, MCS)
(Used in Rapidly Evolving Severe Convective Events; VCP212 in widespread events)
VCP21 / VCP121 / VCP221 - Stratiform / Tropical Systems Precipitation Mode
Short Pulse - 9 Elevation Scans in 6.0 Minutes
Lowest Scan: 0.5 Degree Elevation / Highest Scan: 19.5 Degree Elevation
(Scans at .5 / 1.5 / 2.4 / 3.4 / 4.3 / 6.0 / 9.9 / 14.6 / 19.5 Degrees)
Detection of.. Stratiform Precipitation.. Tropical Systems/Funnels
(Used in Non-Severe Convective / Stratiform; VCP121 choice for hurricanes)
CLEAR AIR MODES
VCP31 / Clear Air Mode
Long Pulse (4.7 microseconds) - 5 Elevation Scans in 10.0 Minutes
Lowest Scan: 0.5 Degree Elevation / Highest Scan: 4.5 Degree Elevation
(Scans at .5 / 1.5 / 2.5 / 3.5 / 4.5 Degrees)
Detection of.. Biological Targets.. More Detailed Boundary Layer Moisture/Temperature
Discontinuities.. Clear-air, Snow and Light Stratiform Precipitation (Best Sensitivity of the Clear
Air Modes)
VCP32 / Clear Air Mode (NWS Default for Clear Air Mode)
Short Pulse - 5 Elevation Scans in 10.0 Minutes
Lowest Scan: 0.5 Degree Elevation / Highest Scan: 4.5 Degree Elevation
(Scans at .5 / 1.5 / 2.5 / 3.5 / 4.5 Degrees)
Detection of.. Clear-air, Snow and Light Stratiform Precipitation
© 2010 Troy Kim m el (em ail: tkim m el@ m ail.utexas.edu ), Lecturer / Studies in W eather and Clim ate
Departm ent of Geography and the Environm ent, University of Texas at Austin
19
WSR88D Z/R Relationships
Tropical Z/R
Convective Z/R
Stratiform Z/R
Winter Weather (Cool Season) Z/R
WSR88D Most Commonly Used Products
Base Reflectivity (BREF)... Corresponds to the intensity of the radiation (energy) that is scattered or
reflected back to the radar by whatever targets are in the radar beam at a given location in the
atmosphere. Targets can be hydrometeors (i.e., rain droplets) or other non meteorological targets (i.e.,
birds, airplanes, dust).
Composite Reflectivity (CREF)... Corresponds to the maximum base reflectivity value that occurs in a
given vertical column in the radar umbrella. Composite reflectivity is good in that it gives a plan view of
the most intense parts of thunderstorms and when compared with base reflectivity data, it can be used
to get a “3D” view of thunderstorms.
Base Velocity (BVEL)... Corresponds to the average radial velocity (along the direction of the radar
beam - toward or away from the radar) of the targets in the radar beam at a given location in the
atmosphere. Positive values (warm colors / reds) denote outbound velocities while negative values
(cold colors / greens) denote inward directed velocities. Base velocity data is useful in examining squall
lines and straight line thunderstorm wind events.
Storm Relative Velocity (SRVEL)... Corresponds to base velocity data with the average motion of all
storm centroids subtracted out. Storm relative radial velocity is useful in detecting mesocyclones and
other circulation patterns.
Rainfall Accumulation Products (RAIN)... Attempts to estimate the amount of rainfall that has fallen
in a given area in the radar’s umbrella by making certain assumptions about the number and kind of
raindrops it detects. There are limitations to this product and it should be used in combination with
other radar products and ground based rain gauge networks. There are three products in this
classification: (1) a running 1 hour rainfall total, (2) a running 3 hour rainfall total, and (3) a running
storm total rainfall accumulation (reset by the NWS after a major event ends).
Vertically Integrated Liquid (VIL)... A calculation that converts a “column” of reflectivity into its liquid
water equivalent. It is very important to note that VIL can be quite seasonal and geographically
correlated to hail size.
Echo Tops (ECHO)... Corresponds to the average elevation where the top of a given precipitation core
is located.
VAD Wind Profile (VWP)... Time series of the estimate of the horizontal wind at specific heights above
the radar. It is useful in diagnosing location and structure of fronts, moisture moving northward from the
Gulf of Mexico and other meteorological phenomena.
Courtesy: Oklahoma Climatological Survey
Radar Product Information - Courtesy of the Oklahoma Climatological Survey
20
Quick Reference VCP Comparison Table for RPG Operators
Slices
Tilts /
Time*
14
VCP
Description
11
Legacy
211
SZ-2,
improved
split cuts
12
Faster
Updates,
better
vertical
converage
in
5
mins
14
in
4½
mins
212
21
9
in
121
6
mins
221
5
in
31
10
mins
32
*VCP update times are approximate.
Usage
Limitations
Severe and non-severe convective
events. Local 11 has Rmax=80nm.
Remote 11 has Rmax=94nm.
Widespread precipitation events with
embedded, severe convective activity
(e.g. MCS, hurricane). Significantly
reduces range-obscured V/SW data
when compared to VCP 11.
Rapidly evolving, severe convective
events. Extra low elevation angles
increase low-level vertical resolution
when compared to VCP 11.
Rapidly evolving, widespread severe
convective events (e.g. squall line,
SZ-2,
MCS). Increased low-level vertical
improved resolution compared to VCP 11.
split cuts Significantly reduces range-obscured
V/SW data when compared to VCP 12.
Non-severe convective precipitation
events. Local 21 has Rmax=80nm.
Legacy
Remote 21 has Rmax=94nm.
VCP of choice for hurricanes.
MPDA
Widespread stratiform precipitation
applied to events. Significantly reduces rangesplit cuts obscured V/SW data when compared to
VCP 21. Updates in about 5 min.
Widespread precipitation events with
embedded, possibly severe convective
SZ-2,
activity (e.g. MCS, hurricane). Further
improved reduces range-obscured V/SW data
split cuts when compared to VCP 121. 5 min
updates.
Clear-air, snow, and light stratiform
Long Pulse precipitation. Best sensitivity. Detailed
boundary layer structure often evident.
Clear-air, snow, and light stratiform
Short Pulse precipitation.
WDTB RPS21List Decision Aid:
Dec 2006
Fewer low elevation angles make this VCP less
effective for long-range detection of storm features
when compared to VCPs 12 and 212
All Bins clutter suppression is NOT
recommended. PRFs are not editable for
SZ-2 (Split Cut) tilts.
High antenna rotation rates decrease the
effectiveness of clutter filtering, increase the
likelihood of bias, and slightly decrease
accuracy of the base data estimates.
All Bins clutter suppression is NOT
recommended. PRFs are not editable for SZ-2
(Split Cut) tilts. High antenna rotation rates
decrease the effectiveness of clutter filtering,
increase the likelihood of bias, and slightly
decrease accuracy of the base data estimates.
Gaps in coverage above 5°, 6 min updates.
PRFs are not editable for any tilt.
Gaps in coverage above 5°.
All Bins clutter suppression is NOT
recommended. PRFs are not editable for SZ-2
(Split Cut) tilts. Gaps in coverage above 5°.
Susceptible to velocity dealiasing failures. No
coverage above 5°. Rapidly developing
convective echoes aloft might be missed.
No coverage above 5°. Rapidly developing
convective echoes aloft might be missed.
http://www.wdtb.noaa.gov/tools/RPS
Convergence / Confluence / Difluence / Divergence?
What does it all mean?
Often times, when we discuss the concepts of atmospheric difluence and confluence as well as of atmospheric
divergence and convergence, we tend to misunderstand (at best) and misuse (at worst) the terms.
Let’s take a look at the terms and what they mean...
Convergence:
The mathematical concept that refers to a net gain of mass at a level, in a
layer or in a column (in our atmosphere). Convergence is comprised of
speed convergence, which is faster wind speeds upstream from slower wind
speeds downstream and directional convergence (has come to be referred to
as “confluence”). This is very much like a entrance ramp on a interstate
highway. Your ability to merge onto the interstate is based upon the relative
speeds of the cars on the highway and the cars on the ramp. In other words,
just because you have an on ramp (confluence) , it doesn't necessarily mean
you have a traffic jam even though you can (through speed convergence).
In our atmosphere, to compensate for the resulting "excess," convergence
may result in vertical motion. It would result in upward forcing if convergence is at
low levels or downward forcing (subsidence) if convergence is at high levels.
Upward forcing from low-level convergence increases the potential for
thunderstorm development (when other factors, such as instability, are favorable).
Divergence:
The mathematical concept that refers to a net loss of mass at a level, in a layer
or in a column (in our atmosphere). Divergence is comprised of speed divergence,
which is slower wind speeds upstream from faster wind speeds downstream and
directional divergence (has come to be referred to as “difluence.”) This is very
much like a interstate highway off ramp. Your ability to exit is based upon the
relative speeds of the cars on the interstate highway and the cars on the access
road. In other words, just because you have an off ramp (difluence), it doesn't
mean you relieve the traffic jam, although, it's a start!
When divergence, in general, occurs in the Earth’s atmosphere near the surface,
sinking motion will occur in the center of the divergence and it can favor a more
stable weather pattern with a clear, dry weather pattern. Divergence at upper
levels of the atmosphere may enhance upward motion and hence the potential for
thunderstorm development (if other factors also are favorable).
Let’s define these terms as well:
Confluence:
A pattern of wind flow in which the air streamlines flow inward toward an axis oriented parallel to the general wind
flow downstream. Confluence causes a net gain of air molecules at the level of the atmosphere where the confluence is
occurring. The opposite of difluence. Please note that confluence is not the same as convergence. Winds often
accelerate as they enter a confluent zone, resulting in speed divergence which offsets the (apparent) converging effect
of the confluent flow.
Difluence:
A pattern of wind flow in which air streamlines move outward, in a fan-out pattern, away from a central axis that is
oriented parallel to the general wind flow downstream. Difluence causes a net loss of air molecules at the level of the
atmosphere where the difluence is occurring. The opposite of confluence. Difluence in an upper level wind field is
considered a favorable condition for severe thunderstorm development (if other parameters are also favorable) but
difluence is not the same as divergence. In a difluent flow, winds normally decelerate as they move through the region of
difluence, resulting in speed convergence which offsets the apparent diverging effect of the difluent flow.
Source/Courtesy:
Dr. Kevin Kloesel, University of Oklahoma
Michael Branick, NW S/Norman, OK. NOAA Technical Memorandum NWS SR-145, A Comprehensive Glossary of Weather Terms for Storm Spotters
www.eotsweb/org
www.theweatherprediction.com for illustration
http://www.flame.org/~cdoswell/peeves/Pet_Peeves.html
22
Vorticity Basics
(Based on and courtesy of Haby Hints #56, http://www.theweatherprediction.com/habyhints/56/ ;
Prepared by Jeff Haby, Meteorologist / Instructor, Mississippi State University)
Important things to know...
(1) Vorticity is a clockwise or counterclockwise spin in the troposphere. This can be along a
vertical axis (up and down) or along a horizontal axis (cross ways) through the atmosphere.
(2) Synoptic scale vorticity is analyzed and plotted on the 500-mb constant height chart.
This is also termed “vertical vorticity” (the spin is in relation to a vertical axis). This vorticity is
caused by troughs and ridges and other embedded waves or height centers (speed and
directional wind changes in relation to a vertical axis). A wind flow through a vorticity gradient
will produce regions of PVA (Positive Vorticity Advection) - sometimes noted with an “X” on the
500mb chart and indicating a counterclockwise spin - and NVA (Negative Vorticity Advection) sometimes noted with a “N” on the 500mb chart and indicating a clockwise spin. Note that PVA
(“X” on map - CCW spin) contributes to rising, more unstable air while NVA (“N” on map - CW
spin) contributes to sinking, more stable air.
(4) Vorticity caused by a change in wind direction or wind speed with height is termed
“horizontal vorticity” (the spin is in relation to a horizontal axis). Horizontal vorticity is most
important in the planetary boundary or friction layer (low-levels of atmosphere); i.e. if the wind
at the surface is southeast at 30 knots and the wind speed at 700 mb is west southwest at 60
knots, there will be a large amount of speed and directional (veering) shear with height and
therefore a large amount of horizontal vorticity.
“Streamwise vorticity” is the amount of horizontal vorticity that is parallel to storm inflow. Storm
inflow is the velocity of the low-level wind moving toward a thunderstorm. Helicity is the amount
of streamwise vorticity that is available to be ingested by a thunderstorm. Helicity is a great
index to use to assess horizontal vorticity and the threat for rotating thunderstorms.
In summary...
Vertical positive vorticity (CCW spin) contributes to upper level divergence in the PVA region
and thus rising air in the atmosphere. Vertical negative vorticity (CW spin) contributes to
upper level convergence in the NVA region and thus sinking motion in the atmosphere.
Horizontal vorticity, related to a substantial veering of the wind direction and an increase in
wind speed in the lowest few thousand feet of the atmosphere, is important to severe weather
(large values of horizontal vorticity lead to large values of streamwise vorticity, or helicity, that
is available to be ingested by a thunderstorm.. which increases the likelihood of tornadoes in
association with supercell thunderstorms).
Both vorticity types are a clockwise or counterclockwise rotation, but one is in relation to a
vertical axis and the other a horizontal axis.
23
24
25
A Basic Primer
on Thunderstorms
Determining Thunderstorm Types...
Ingredients: Atmospheric Instability
Moisture (mT airmasses)
Atmospheric Lift
Types: Single Cells
Multicell Clusters
Multicell Lines
Supercells
Stages: Cumulus (Updrafts dominate)
Mature (Updrafts/downdrafts coexist)
Dissipating (Downdrafts dominate)
Climatology: At any given moment, 2000 individual thunderstorms are in progress worldwide. Of those...
> 95% are NON-SEVERE
(hail < 1" in diameter,
straight line thunderstorm winds
less than 50 knots/58 mph)
< 5% are SEVERE
(hail equal to or > 1" in diameter,
straight line thunderstorm winds of
50 knots/58 mph or higher,
the presence of a tornado)
Formation: On average, found
within mT airmass
Formation: On average, found on
boundaries of mT airmass
Structure:
Structure:
Lifetime:
1 to 1 1/2 hours
Lifetime:
Can last a long time
Characterized by
vertical cloud towers
(downdrafts cut off
updrafts rapidly)
Characterized by
tilted well defined long
lasting cloud towers
with separated
updraft and downdraft)
Hazards:
- Dangerous lightning
- Brief heavy rain
- Hail < 1" in diameter
- Straight line thunderstorm (downdraft)
winds of less than 50 knots/58 mph
- Rarely brief weak tornadoes
Hazards:
- Dangerous lightning (more frequent)
- Heavy rain (flooding more frequent)
- Large, potentially damaging hail 1" or more
in diameter
- Damaging straight line thunderstorm (downdraft)
winds of 50 knots/58 mph or greater
- Longer lasting, more significant tornadoes
Other Thunderstorm Phenomena....
- Supercells
- Mesoscale Convective Systems (MCSs)
- Mesoscale Convective Complexes (MCCs)
- Squall Line
- Bow Echoes
- Mesocyclones
- Bounded Weak Echo Region (BWER)
- Derechos
- Downbursts (Microbursts & Macrobursts)
COPYRIGHT: Troy M. Kimmel, Jr.
26
27
A Basic Primer
on Severe / Inclement Weather Hazards
COPYRIGHT: Troy M. Kimmel, Jr.
Lightning:
Forms as a result of separation of charges created because of the presence of ice crystals and cloud droplets in the strong updrafts and
downdrafts
Begins at the very end of the cumulus stage into the mature stage of thunderstorm development
100 lightning strikes every second around the world
On average in the US, about 100 deaths and 1000 injuries as a result of lightning
On average in the US, $25 million in lightning damage every year
A bolt of lightning is about the diameter of a pencil
Within the lightning bolt, it is about five times the temperature of the outer surface of the Sun (54,000º F)
Lightning can strike up to 10 to 20 miles away from the parent thunderstorm (“bolt from the blue”)
Time it!! Count between stroke and associated thunder.. every five seconds equal one mile away
Types of lightning:
Cloud to ground (LTGCG)
Cloud to cloud (LTGCC)
Cloud to water (LTGCW)
Cloud to air (LTGCA)
Intracloud (LTGIC)
... or combinations (LTGICCCCG)
Most frequent: Cloud to Cloud and Intracloud (60%)
Most deadly: Cloud to Ground (20%)
Frequency of lightning:
Occasional (OCNL)
Frequent (FQT)
Continuous (CNS)
Less than 1 flash per minute
About 1 to 6 flashes per minute
More than 6 flashes per minute
Positive (less frequent but more deadly) and negative charges are present
In aviation weather observations, thunderstorms are officially observed when thunder is first heard and end 15 minutes after last thunder is
heard
Florida is the lightning “capital” of the US
Other lightning related terms: Heat lightning
Sheet lightning
Ball lightning
Hail:
Hail size (and thunderstorm severity) is entirely dependent of thunderstorms updraft and downdraft speed
1" diameter (quarter size) or larger hail is considered “severe”
When considering hail size, free fall velocity of hail stones is important when considering damage
Largest hail often falls northeast of tornadoes
In US, hail occurrence is most frequent central and southern plains west northwestward to the front range of the Rockies
Mainly responsible for property (home, automobile) and agricultural damage in the US; few injuries and deaths (not necessarily true world wide)
Largest hailstone in US history: 7 inches in diameter (almost as large as soccer ball) and 18 3/4" in circumference
in south central Nebraska at Aurora on June 22, 2003
Straight Line Thunderstorm Winds:
Much more common than tornadoes (although most people think thunderstorm wind damage is caused by tornadoes)
Strong downdraft winds from thunderstorms (divergent wind pattern)
Major threat to aviation
Referred to, in general, as “downbursts”
Macroburst - Downburst “foot print” of greater than 2.5 miles in diameter
Microburst - Downburst “foot print” of 2.5 miles or less in diameter
Wet and dry downbursts occur
Tornadoes:
A violently rotating column of air extending from the base of a cumulonimbus cloud (severe thunderstorm) and reaching the earths surface
Narrow path with a convergent damage pattern
(For more information, see “A Basic Primer on Tornadoes”)
Flash Floods:
One of the top weather killers in the US
General public does not understand the power of moving water
Types of flooding: River flooding
Flash flooding
South central Texas is considered the flash flood capital of the US (subsoil limestone layers, urbanization, and hilly nature of Texas Hill Country)
Summer Heat:
The number one weather killer in the US
Heat related illnesses and heat stroke (signs: we stop sweating)
We sweat in order to stay cool (evaporative cooling); this evaporative cooling is dependent on the amount of environmental moisture present
Heat stress index
Winter Cold:
Hypothermia and frostbite
Wind chill charts
28
COPYRIGHT: Troy M. Kimmel, Jr.
Reporting Hail Sizes
Always remember that hail diameter should be reported to
the National Weather Service in inch size diameter. This
chart associates commonly sized objects (left column) with
what should be reported in inch size diameter (right column).
Hail Sizes
(Common Objects)
Hail Sizes
(Please Report as...)
Freefall
Velocity
.... Non Severe Reports ....
Pea Size........................
1/4 inch or smaller (0.25 inch)... 25 mph
Pinto Bean Size.............
3/8 inch (0.40 inch).................... 30 mph
Regular Marble Size......
1/2 inch (0.50 inch).................... 35 mph
Dime Size......................
5/8 inch (0.60 inch).................... 40 mph
Penny Size.................... 3/4 inch (0.75 inch)................... 43 mph
Nickle Size....................
7/8 inch (0.88 inch)................... 47 mph
.... Severe Reports ....
Quarter Size..................
Half Dollar Size.............
Ping Pong Ball Size......
Golfball Size.................
Hen Egg Size................
Racket Ball Size............
Tennis Ball Size............
Baseball Size................
Tea Cup Size................
.............
.............
.............
.............
.............
Grapefruit/Softball Size..
DVD/CD Size................
..............
1 inch (1.00 inch)......................
1 1/4 inch (1.25 inch)................
1 1/2 inch (1.50 inch)................
1 3/4 inch (1.75 inch)................
2 inches (2.00 inches)..............
2 1/4 inches (2.25 inch)............
2 1/2 inches (2.50 inch)............
2 3/4 inches (2.75 inch)............
3 inches (3.00 inch)..................
3 1/4 inches (3.25 inch)............
3 1/2 inches (3.50 inch)............
3 3/4 inches (3.75 inch)............
4 inches (4.00 inch)..................
4 1/4 inches (4.25 inch)............
4 1/2 inches (4.50 inch)............
4 3/4 inches (4.75 inch)............
5 inches (5.00 inch)..................
29
50 mph
56 mph
61 mph
66 mph
72 mph
76 mph
80 mph
85 mph
89 mph
94 mph
98 mph
102 mph
106 mph
112 mph
117 mph
122 mph
125 mph
COPYRIGHT: Troy M. Kimmel, Jr.
A Basic Primer
on Tornadoes
Definition: A rapidly rotating column of air extending from a cumulonimbus (thunderstorm) cloud
and touching the ground. Consisting of condensation (cloud) and debris, this rotating column
of air may not always be visible; however, if a debris cloud is visible near the ground, then
it is a tornado. If not, this is referred to as a “funnel cloud.”
Ingredients: mT air mass (warm, moist air)
Extremely unstable air mass
Strong lifting mechanism (mid latitude frontal cyclones, cold fronts, dry lines)
Initial temperature inversion creates a “lid” on atmosphere which is then
violently broken by strong lifting mechanism above
Categories: Strength Scale (Weak, strong and violent)
Damage Scale (Enhanced Fujita Scale)
Development:
- Wind shear aloft
Wind direction veering with height (strongly shifting clockwise with height in lowest 10,000 feet)
Wind speed increasing with height (strongly increasing in lowest 10,000 feet)
- Wind speed increase causes horizontal rolls to develop
- Strong updrafts, as thunderstorm develops, cause horizontal rolls to be stretched vertically
- The resulting rotating updraft is referred to as a mesocyclone
- In less than 20% of all mesocyclones, a tornado starts to develop usually at mid levels
of the thunderstorm (10,000 to 20,000 feet above the ground)
- Funnel / strong circulation extends downward in thunderstorm
- Air behinds to rush rapidly into the vortex and rises, expands and cools
- When and if the rapid circulation reaches the ground, it’s then a tornado
- Radial wind is always directed into the center of the tornado (convergent damage pattern)
- Some sinking motion in the middle of the tornado (very small area)
- Most tornadoes in the northern hemisphere rotate counter clockwise (Coriolis Force)
- The temperature profile in tornadoes is largely unknown
Climatology:
- Less than 1% of all thunderstorms world wide produce tornadoes
- Tornadoes are more frequent in North America than any other area of the world
- Atmospheric pressure, in the strongest tornadoes, is thought to be about 10% less than
standard atmospheric pressure
- Tornadoes have occurred in every state of the US, but are most frequent in the
southern and central US plains/Mississippi Valley
- Tornadoes most frequent between 3 and 7 pm local time in the US
- Annually, 50% of US tornadoes occur in April, May and June
- Annually, 75% of US tornadoes occur between March and July
- Annually in the US, May is, on average, the month with the greatest number of tornadoes
- Annually in the US, April has, on average, the most violent tornadoes
- Average US tornado movement is from the southwest to the northeast
(Exception: Texas - tropical cyclone influence - east /southeast to west /northwest)
- Average US tornado forward speed is about 30 mph
- Annually, on average here in the US, there are about 1300 tornadoes
Of these 1300 tornadoes, 80% are weak, 19% are strong and 1% or less are violent
30
Tornado Strength Scale:
COPYRIGHT: Troy M. Kimmel, Jr.
Weak Tornadoes:
Thin, Rope like Appearance (80% of all tornadoes) – EF0, EF1 damage equivalent (appx)
Less than 5% of all US Tornado Fatalities
Lifetime Less than 10 Minutes
Wind 65 to 110 mph / Path Length 3 miles / Path Width 90 Yards
Average Warning Statistics
Strong Tornadoes:
More Classic, Wider Funnel (19% of all tornadoes) – EF2, EF3 damage equivalent (appx)
Less than 30% of all US Tornado Fatalities
Lifetime 20 Minutes or More
Wind 111 to 165 mph / Path Length 15+ Miles / Path Width 200 Yards
Very Good Warning Statistics
Violent Tornadoes:
Very Wide Wedge Funnel (< 1% of all tornadoes) – EF4, EF5 damage equivalent (appx)
70% of all US Tornado Fatalities
Lifetime 60 Minutes or More
Wind 166 to 318 mph / Path Length 25+ Miles / Path Width 600 Yards
Excellent Warning Statistics
Tornado Damage Scale:
Enhanced Fujita Scale (Replaced Fujita Scale 1 February 2007)
(Courtesy: Wikipedia)
EF0 Damage - Light damage / 65 to 85 mph (three second gust)
Peels surface off some roofs; some damage to gutters or siding;
branches broken off trees; shallow-rooted trees pushed over.
EF1 Damage - Moderate damage / 86 to 110 mph (three second gust)
Roofs severely stripped; mobile homes overturned or badly damaged; loss of
exterior doors; windows and other glass broken.
EF2 Damage - Considerable damage / 111 to 135 mph (three second gust)
Roofs torn off well-constructed houses; foundations of frame homes shifted;
mobile homes completely destroyed; large trees snapped or uprooted;
light-object missiles generated; cars lifted off ground.
EF3 Damage - Severe damage / 136 to 165 mph (three second gust).
Entire stories of well-constructed houses destroyed; severe damage to large
buildings such as shopping malls; trains overturned; trees debarked; heavy
cars lifted off the ground and thrown; structures with weak foundations blown
away some distance.
EF4 Damage - Devastating damage / 166 to 200 mph (three second gust)
Well-constructed houses and whole frame houses completely leveled; cars
thrown and small missiles generated.
EF5 Damage - Incredible damage / 201 to 318 mph (three second gust)
Strong frame houses leveled off foundations and swept away; automobile
sized missiles fly through the air in excess of 119 yds; high-rise buildings
have significant structural deformation; incredible phenomena will occur.
31
Tornadoes, Landspouts, Gustnadoes,
Waterspouts, Funnel Clouds and Wall Clouds...
How Do You Tell Them Apart?
Tornado This is a violently rotating column of air that is in contact with both the surface of the earth
and a cumulonimbus (thunderstorm) cloud. The presence of a tornado is one of the
NWS criteria (along with 1" or larger diameter hail at surface and/or thunderstorm wind
gusts at or above 58 mph) for classifying a thunderstorm as being “severe.” Tornadoes are
often referred to as “twisters.” Since the tornado is composed of cloud droplets as well as
debris, you may not always see a visible connection between the cloud and the ground
especially at the beginning of the tornado lifetime.. but remember that as long as the
violently rotating column of air is present, you do have a tornado. (EF0 to EF5 damage)
Landspout This feature, given its name by severe thunderstorm/tornado researcher Howie Bluestein,
denotes a kind of tornado that is not associated with the mesocyclone of a thunderstorm.
The landspout looks, in many ways, like Keys waterspout and like them, they tend to
develop during growth stage of cumulus clouds. Formed by boundary layer horizontal
vorticity that is stretched upwards into the updraft. They are smaller and weaker than
mesocyclone tornadoes but can last up to 15 minutes. They tend to be found in more
semi-arid areas. Associated with higher cloud bases with abundant low level instability
often in the high plains of the USA. (EF0 to EF3 damage)
Gustnado Specific type of short lived low level cloud (non mesocyclone) that can be present in a
severe or non severe thunderstorm. It usually does not extend all the way to the close
base of the thunderstorm and lasts from a few seconds to a few minutes. It is usually
found on front edge of thunderstorm and is downdraft dominated. Sometimes referred to
as “spin up” tornadoes and are most often found in the Great Plains of the USA.
(EF0 to EF1 damage)
Funnel Cloud This is a funnel-shaped cloud of condensed water droplets, associated with a rotating
column of wind and extending from the base of a cloud (usually a cumulonimbus or
towering cumulus cloud) but not reaching the ground or a water surface. Most tornadoes
begin as funnel clouds, but many funnel clouds do not make ground contact and so do not
become tornadoes.
Waterspout This is, in a very basic sense, a tornado over water with the rapidly rotating column of air
actually touching the water surface. However, most waterspouts, that are not associated
with mesocyclones, are relatively weak (winds less than 67 mph) and associated with
cloud lines of cumulus congestus and/or cumulonimbus clouds. They usually occur in
tropical/sub-tropical areas and tend to occur closer to coastlines rather than in areas
further away from land. Waterspouts have a five-part life cycle: formation of a dark spot on
the water surface, spiral pattern on the water surface, formation of a spray ring,
development of the visible condensation funnel, and ultimately decay.
A relatively small number of waterspouts are associated with severe thunderstorms and
their mesocyclone (rotating updraft). These are much stronger and are basically the same
as spring season Great Plains severe thunderstorms.
Wall Cloud This is an isolated lowering beneath the updraft of a strong thunderstorm. It results from
the rapid rising of air of the updraft and the resultant condensation as the air rises and
cools. If the wall cloud rotates, it indicates a rotating updraft and is the general area where
tornadogenesis is favored.
Text Credits: Wikipedia, American Meteorological Society , NOAA/National Weather Serv ice
Photo Credits: NOAA/National Weather Serv ice, DOGONews, Ron Elv ington, Denv er Post, FloridaSportsman.com
32
TUPELO (MS) EF-3 TORNADO
TUPELO (MS) REGIONAL AIRPORT ASOS WEATHER OBSERVATIONS
1900z-1945z (200pm-245pm CDT) TUESDAY / 28 APRIL 2014
Prepared by Troy Kimmel
University / Incident Meteorologist, Senior Lecturer (Studies in Weather and Climate), University of Texas
[email protected]
.. 5 min METAR DATA data ...
5-MIN KTUP 281905Z 24004KT 10SM BKN035 25/19 A2963 620 68 2000 240/04 RMK AO2 LTG DSNT SW-N T02500189
5-MIN KTUP 281910Z 24003KT 10SM VCTS BKN035 25/19 A2962 620 68 2000 240/03 RMK AO2 LTG DSNT SW-N T02500189
5-MIN KTUP 281915Z 00000KT 10SM VCTS OVC035 25/19 A2962 620 68 2000 000/00 RMK AO2 LTG DSNT SW-N T02500189
5-MIN KTUP 281920Z 00000KT 10SM VCTS OVC035 25/19 A2961 640 68 2000 000/00 RMK AO2 LTG DSNT SW-N PRESFR T02500189
5-MIN KTUP 281925Z AUTO 06006KT 10SM TS OVC037 24/19 A2961 630 71 1900 070/06 RMK AO2 LTG DSNT SW-NW TSB21 T02440189
5-MIN KTUP 281930Z AUTO 07008KT 10SM TS BKN037 OVC047 24/19 A2960 640 76 1900 070/08 RMK AO2 LTG DSNT SW-N TSB21 T02390194
5-MIN KTUP 281935Z AUTO 10017KT 10SM TS BKN037 BKN047 OVC095 24/19 A2953 720 73 2000 100/17 RMK AO2 LTG DSNT SW-N TSB21 PRESFR
T02440194
5-MIN KTUP 281940Z AUTO 08026G32KT 10SM TS SCT037 BKN049 OVC090 24/19 A2941 830 71 2100 090/26G32 RMK AO2 PK WND 09032/1940 LTG DSNT
SW-N TSB21 PRESFR T02440189
5-MIN KTUP 281945Z AUTO 28026G39KT 8SM TS FEW017 BKN039 OVC070 24/19 A2948 760 73 2000 280/26G39 RMK AO2 PK WND 29039/1945 LTG DSNT
ALQDS TSB21 T02390189
--ASOS DOWN--OUT OF SERVICE-- (POWER OUTAGE)-5-MIN KTUP 282240Z AUTO M M M M / M RMK AO2 LTG DSNT ALQDS RAB47 TSB21E48 PNO $
.. 1 min ASOS Weather/Precipitation/Pressure Data ...
93862 KTUP TUP 2014042813001900 NP 0000 0.00
93862 KTUP TUP 2014042813011901 NP 0000 0.00
93862 KTUP TUP 2014042813021902 NP 0000 0.00
93862 KTUP TUP 2014042813031903 NP 0000 0.00
93862 KTUP TUP 2014042813041904 NP 0000 0.00
93862 KTUP TUP 2014042813051905 NP 0000 0.00
93862 KTUP TUP 2014042813061906 NP 0000 0.00
93862 KTUP TUP 2014042813071907 NP 0000 0.00
93862 KTUP TUP 2014042813081908 NP 0000 0.00
93862 KTUP TUP 2014042813091909 NP 0000 0.00
93862 KTUP TUP 2014042813101910 NP 0001V 0.00
93862 KTUP TUP 2014042813111911 NP 0001V 0.00
93862 KTUP TUP 2014042813121912 NP 0001V 0.00
93862 KTUP TUP 2014042813131913 NP 0001V 0.00
93862 KTUP TUP 2014042813141914 NP 0001V 0.00
93862 KTUP TUP 2014042813151915 NP 0001V 0.00
93862 KTUP TUP 2014042813161916 NP 0001V 0.00
93862 KTUP TUP 2014042813171917 NP 0001V 0.00
93862 KTUP TUP 2014042813181918 NP 0001V 0.00
93862 KTUP TUP 2014042813191919 NP 0001V 0.00
93862 KTUP TUP 2014042813201920 NP 0001V 0.00
93862 KTUP TUP 2014042813211921 NP 0001 0.00
93862 KTUP TUP 2014042813221922 NP 0001 0.00
93862 KTUP TUP 2014042813231923 NP 0001 0.00
93862 KTUP TUP 2014042813241924 NP 0001 0.00
93862 KTUP TUP 2014042813251925 NP 0001 0.00
93862 KTUP TUP 2014042813261926 NP 0001 0.00
93862 KTUP TUP 2014042813271927 NP 0001 0.00
93862 KTUP TUP 2014042813281928 NP 0001 0.00
93862 KTUP TUP 2014042813291929 NP 0001 0.00
93862 KTUP TUP 2014042813301930 NP 0001 0.00
93862 KTUP TUP 2014042813311931 NP 0001 0.00
93862 KTUP TUP 2014042813321932 NP 0001 0.00
93862 KTUP TUP 2014042813331933 NP 0001 0.00
93862 KTUP TUP 2014042813341934 NP 0001 0.00
93862 KTUP TUP 2014042813351935 NP 0001 0.00
93862 KTUP TUP 2014042813361936 NP 0001 0.00
93862 KTUP TUP 2014042813371937 NP 0001 0.00
93862 KTUP TUP 2014042813381938 NP 0001 0.00
93862 KTUP TUP 2014042813391939 NP 0001 0.00
93862 KTUP TUP 2014042813401940 NP 0001 0.00
93862 KTUP TUP 2014042813411941 NP 0001 0.00
93862 KTUP TUP 2014042813421942 NP 0001 0.00
93862 KTUP TUP 2014042813431943 NP 0001 0.00
93862 KTUP TUP 2014042813441944 NP 0001 0.00
93862 KTUP TUP 2014042813451945 ?2 0001 0.00
93862 KTUP TUP 2014042813461946 R 0001 0.00
93862 KTUP TUP 2014042813471947 R
M
0.00
93862 KTUP TUP 2014042813481948 R+ M 0.00
93862 KTUP TUP 2014042813491949 R+ M 0.00
93862 KTUP TUP 2014042813501950 R+ M 0.07
--ASOS DOWN--OUT OF SERVICE-- (POWER OUTAGE)-93862 KTUP TUP2014042816392239 M
M
93862 KTUP TUP2014042816402240 M 0000
93862 KTUP TUP2014042816412241 NP 0000
29.270 29.280 29.281 76 67
29.272 29.282 29.282 76 67
29.268 29.278 29.279 77 66
29.262 29.272 29.272 77 66
29.257 29.267 29.267 77 66
29.255 29.265 29.265 77 66
29.253 29.263 29.263 77 66
29.251 29.261 29.261 77 66
29.249 29.259 29.259 77 66
29.248 29.258 29.258 77 66
29.247 29.257 29.257 77 66
29.247 29.257 29.257 77 66
29.248 29.259 29.259 77 66
29.250 29.260 29.260 77 66
29.250 29.260 29.260 77 66
29.248 29.258 29.258 77 66
29.245 29.255 29.255 77 66
29.241 29.251 29.251 77 67
29.237 29.247 29.247 77 66
29.234 29.245 29.245 77 66
29.232 29.242 29.242 77 66
29.229 29.239 29.239 76 66
29.226 29.236 29.236 76 66
29.224 29.235 29.235 76 66
29.228 29.239 29.239 76 67
29.237 29.247 29.248 76 67
29.245 29.255 29.255 75 67
29.247 29.257 29.257 75 67
29.241 29.252 29.252 75 67
29.234 29.244 29.244 75 67
29.227 29.238 29.238 75 67
29.218 29.229 29.229 75 67
29.206 29.217 29.217 76 67
29.190 29.201 29.201 76 67
29.170 29.180 29.180 76 67
29.151 29.162 29.161 76 66
29.132 29.142 29.142 76 66
29.112 29.122 29.122 76 66
29.088 29.099 29.098 76 66
29.057 29.068 29.068 76 66
29.033 29.043 29.043 76 66
29.021 29.031 29.031 76 66
29.039 29.049 29.049 76 66
29.107 29.117 29.117 76 67
29.136 29.146 29.146 75 66
29.108 29.118 29.120 74 66
29.153 29.162 29.163 73 67
29.193 29.202 29.204 70 67
29.185 29.195 29.195 69 66
29.186 29.196 29.196 69 66
29.188 29.199 29.199 70 67
M
M
M
M
M
M
M
M
M
33
M M
M [ M]
67 [ 65]
C
Courtesy: Tupelo Daily Journal, WTVA-TV,
Skip Talbot/KDR Media, Mike Smith/AccuWeather Enterprises
34
A Basic Primer
on Tropical Cyclones
COPYRIGHT: Troy M. Kimmel, Jr.
Ingredients: Form over the tropical oceans of the World
Surface water temperature of 81 degrees F or higher (at substantial depth)
Weak upper level winds with a anticyclone (high pressure) in upper levels above
(North Atlantic: Southern Oscillation: La Nina years - more likely, El Nino years - less likely)
Stages: Tropical (Easterly) Waves (Open atmospheric wave)
Tropical Depressions (Closed circulation first detected, sustained winds to 34 knots / 39 mph)
Tropical Storms (System named, sustained winds 35 to 64 knots / 40 to 74 mph)
Hurricanes (Sustained winds 65 knots / 75 mph and higher)
(Hurricane Strength and Damage Scale: Saffir-Simpson Scale)
Climatology:
- Seasons... Atlantic Basin - June 1 through November 30
Pacific Basin - May 15 through November 30
- Most TCs develop in the area from 10 degrees N/S of the Equator to 30 degrees N/S of the Equator
- On average, 66% of the worlds TCs occur in the northern hemisphere (warmer waters)
- TCs with sustained winds of 65 knots / 75 mph or higher are referred to as...
Hurricanes in the Atlantic Ocean and eastern/central Pacific Ocean basins
Typhoons in the western Pacific Ocean basin
Cyclones in the Indian Ocean basin
- TCs are “heat machines” transferring excess equatorial heat northward/southward toward poles
- TCs never cross the Equator (from northern to southern hemisphere or vice versa)
- TCs rarely form at more than 30 degrees N/S latitude
- TCs form in all the worlds oceans except the southeastern Pacific and southern Atlantic oceans
- About 80 TCs form annually worldwide; about 60 to 70% become hurricanes/typhoons/cyclones
- TCs are most frequent in the western Pacific Ocean basin
- Names from semi-permanent lists (by basin) created by UN/World Meteorological Organization
Development Areas of the Atlantic Basin (by month)
JULY
AUGUST
OCTOBER
NOVEMBER
JUNE
SEPTEMBER
35
Saffir Simpson Hurricane Wind Scale
COPYRIGHT: Troy M. Kimmel, Jr.
Category One Hurricane
Sustained winds 74-95 mph, 64-82 kt, or 119-153 km/hr
Very dangerous winds will produce some damage
People, livestock, and pets struck by flying or falling debris could be injured or killed. Older (mainly pre-1994
construction) mobile homes could be destroyed, especially if they are not anchored properly as they tend to shift
or roll off their foundations. Newer mobile homes that are anchored properly can sustain damage involving the
removal of shingle or metal roof coverings, and loss of vinyl siding, as well as damage to carports, sunrooms, or
lanais. Some poorly constructed frame homes can experience major damage, involving loss of the roof covering
and damage to gable ends as well as the removal of porch coverings and awnings. Unprotected windows may
break if struck by flying debris. Masonry chimneys can be toppled. Well-constructed frame homes could have
damage to roof shingles, vinyl siding, soffit panels, and gutters. Failure of aluminum, screened-in, swimming
pool enclosures can occur. Some apartment building and shopping center roof coverings could be partially
removed. Industrial buildings can lose roofing and siding especially from windward corners, rakes, and eaves.
Failures to overhead doors and unprotected windows will be common. Windows in high-rise buildings can be
broken by flying debris. Falling and broken glass will pose a significant danger even after the storm. There will
be occasional damage to commercial signage, fences, and canopies. Large branches of trees will snap and
shallow rooted trees can be toppled. Extensive damage to power lines and poles will likely result in power
outages that could last a few to several days. Hurricane Dolly (2008) is an example of a hurricane that brought
Category 1 winds and impacts to South Padre Island, Texas.
Category Two Hurricane
Sustained winds 96-110 mph, 83-95 kt, or 154-177 km/hr
Extremely dangerous winds will cause extensive damage
There is a substantial risk of injury or death to people, livestock, and pets due to flying and falling debris. Older
(mainly pre-1994 construction) mobile homes have a very high chance of being destroyed and the flying debris
generated can shred nearby mobile homes. Newer mobile homes can also be destroyed. Poorly constructed
frame homes have a high chance of having their roof structures removed especially if they are not anchored
properly. Unprotected windows will have a high probability of being broken by flying debris. Well-constructed
frame homes could sustain major roof and siding damage. Failure of aluminum, screened-in, swimming pool
enclosures will be common. There will be a substantial percentage of roof and siding damage to apartment
buildings and industrial buildings. Unreinforced masonry walls can collapse. Windows in high-rise buildings can
be broken by flying debris. Falling and broken glass will pose a significant danger even after the storm.
Commercial signage, fences, and canopies will be damaged and often destroyed. Many shallowly rooted trees
will be snapped or uprooted and block numerous roads. Near-total power loss is expected with outages that
could last from several days to weeks. Potable water could become scarce as filtration systems begin to fail.
Hurricane Frances (2004) is an example of a hurricane that brought Category 2 winds and impacts to coastal
portions of Port St. Lucie, Florida with Category 1 conditions experienced elsewhere in the city.
Category Three Hurricane
Sustained winds 111-130 mph, 96-113 kt, or 178-209 km/hr
Devastating damage will occur
There is a high risk of injury or death to people, livestock, and pets due to flying and falling debris. Nearly all
older (pre-1994) mobile homes will be destroyed. Most newer mobile homes will sustain severe damage with
potential for complete roof failure and wall collapse. Poorly constructed frame homes can be destroyed by the
removal of the roof and exterior walls. Unprotected windows will be broken by flying debris. Well-built frame
homes can experience major damage involving the removal of roof decking and gable ends. There will be a high
percentage of roof covering and siding damage to apartment buildings and industrial buildings. Isolated
structural damage to wood or steel framing can occur. Complete failure of older metal buildings is possible, and
older unreinforced masonry buildings can collapse. Numerous windows will be blown out of high-rise buildings
resulting in falling glass, which will pose a threat for days to weeks after the storm. Most commercial signage,
fences, and canopies will be destroyed. Many trees will be snapped or uprooted, blocking numerous roads.
Electricity and water will be unavailable for several days to a few weeks after the storm passes. Hurricane Ivan
(2004) is an example of a hurricane that brought Category 3 winds and impacts to coastal portions of Gulf
Shores, Alabama with Category 2 conditions experienced elsewhere in this city.
36
Category Four Hurricane
Sustained winds 131-155 mph, 114-135 kt, or 210-249 km/hr).
Catastrophic damage will occur
There is a very high risk of injury or death to people, livestock, and pets due to flying and falling debris. Nearly all
older (pre-1994) mobile homes will be destroyed. A high percentage of newer mobile homes also will be
destroyed. Poorly constructed homes can sustain complete collapse of all walls as well as the loss of the roof
structure. Well-built homes also can sustain severe damage with loss of most of the roof structure and/or some
exterior walls. Extensive damage to roof coverings, windows, and doors will occur. Large amounts of windborne
debris will be lofted into the air. Windborne debris damage will break most unprotected windows and penetrate
some protected windows. There will be a high percentage of structural damage to the top floors of apartment
buildings. Steel frames in older industrial buildings can collapse. There will be a high percentage of collapse to
older unreinforced masonry buildings. Most windows will be blown out of high-rise buildings resulting in falling
glass, which will pose a threat for days to weeks after the storm. Nearly all commercial signage, fences, and
canopies will be destroyed. Most trees will be snapped or uprooted and power poles downed. Fallen trees and
power poles will isolate residential areas. Power outages will last for weeks to possibly months. Long-term water
shortages will increase human suffering. Most of the area will be uninhabitable for weeks or months. Hurricane
Charley (2004) is an example of a hurricane that brought Category 4 winds and impacts to coastal portions of
Punta Gorda, Florida with Category 3 conditions experienced elsewhere in the city.
Category Five Hurricane
Sustained winds greater than 155 mph, greater than 135 kt, or greater than 249 km/hr
Catastrophic damage will occur
People, livestock, and pets are at very high risk of injury or death from flying or falling debris, even if indoors in
mobile homes or framed homes. Almost complete destruction of all mobile homes will occur, regardless of age
or construction. A high percentage of frame homes will be destroyed, with total roof failure and wall collapse.
Extensive damage to roof covers, windows, and doors will occur. Large amounts of windborne debris will be
lofted into the air. Windborne debris damage will occur to nearly all unprotected windows and many protected
windows. Significant damage to wood roof commercial buildings will occur due to loss of roof sheathing.
Complete collapse of many older metal buildings can occur. Most unreinforced masonry walls will fail which can
lead to the collapse of the buildings. A high percentage of industrial buildings and low-rise apartment buildings
will be destroyed. Nearly all windows will be blown out of high-rise buildings resulting in falling glass, which will
pose a threat for days to weeks after the storm. Nearly all commercial signage, fences, and canopies will be
destroyed. Nearly all trees will be snapped or uprooted and power poles downed. Fallen trees and power poles
will isolate residential areas. Power outages will last for weeks to possibly months. Long-term water shortages
will increase human suffering. Most of the area will be uninhabitable for weeks or months. Hurricane Andrew
(1992) is an example of a hurricane that brought Category 5 winds and impacts to coastal portions of Cutler
Ridge, Florida with Category 4 conditions experienced elsewhere in south Miami-Dade County.
Document Courtesy:
NOAA/National Hurricane Center.
37
Varieties of Drought
Courtesy: Office of Texas State Climatologist, Texas A & M University
Meteorological Drought
A significant decrease from the climatologically expected and seasonally averaged
precipitation over a wide area. Palmer developed a numerical long-term drought index
for designating the severity of meteorological drought. Palmer treats drought as a
meteorological phenomenon and defines drought as a prolonged abnormal moisture
drought; that is, drought severity is a function of moisture demand as well as moisture
supply. It depends upon climate because drought is a relative condition and it is a
function of current as well as antecedent weather.
Agricultural Drought
Occurs when soil moisture and rainfall are inadequate during the growing season to
support healthy plant and crop growth to maturity and to prevent extreme crop stress
and wilt. An agricultural drought may well exist even though meteorological drought
does not. That is, soil moisture may be deficient for agricultural needs when the records
show that the total rainfall exceeded the total agricultural needs during the period.
When the rain falls, it’s of prime importance to agricultural production. Too much rain
during the planting season or harvesting season can cause crop failure; growing crops
may wilt because of excess rains or mature crops may ruin in too wet fields before they
can be harvested. On the other hand, a good rain or two during the critical growth
periods may result in good crop yields even when the total rainfall for the year is low.
Hydrological Drought
This is a step further than meteorological drought, usually lasting for several years and
being reflected in the climatological averages of rainfall in areas where it occurs.
Meteorological drought may cause crop destruction, but, if continued long enough,
hydrological drought will be marked by drying up of streams and rivers, depletion of
water stored in surface reservoirs and lakes, cessation of spring flows and decline of
groundwater levels. Hydrological drought is much more far-reaching than
meteorological drought affecting industry as well as agriculture. More rain is required to
end a hydrological drought than any other type of drought.
38
Classications (Degree) of Drought
Courtesy: National Drought Mitigation Center
Abnormally Dry
Going into drought: short term dryness slowing planting and growing of crops and/or
pastures.
Coming out of drought: some lingering water deficits; pastures and/or crops not fully
recovered
(A 1-in-3 year event)
Moderate Drought
Some damage to crops and/or pastures; streams, reservoirs or wells low; some water
shortages developing or imminent; voluntary water use restrictions requested
(A 1-in-5 year event)
Severe Drought
Crop and/or pasture losses likely; water shortages common; water restrictions imposed
(A 1-in-10 year event)
Extreme Drought
Major crop and/or pasture losses; widespread water shortages and/or restrictions
(A 1-in-20 year event)
Exceptional Drought
Exceptional and widespread crop and pasture losses; shortages of water in reservoirs,
streams and wells creating water emergencies
(A 1-in-50 year event)
39
WEATHER SAFETY RULES
COPYRIGHT: Troy M. Kimmel, Jr.
LIGHTNING
- “When Thunder Roars... Go Indoors!!”
If you hear thunder, you are close enough to the thunderstorm to be struck by lightning. Go to safe shelter immediately.
- Go to a steady building or to an automobile. Do not take shelter in small sheds, under isolated trees or in convertible
automobiles. Stay out of boats and away from water.
- If shelter is not available, find a low spot awayfrom trees, fences and poles. In wooded areas, take shelter under shorter trees.
- Telephone lines and metal pipes can conduct electricity. Unplug appliances not necessary for obtaining weather
information. Avoid using the telephone or any electrical appliances. Use the telephone ONLY in emergencies. When in your
home, do not take a bath or shower.
- If you feel your skin begin to tingle or your hair starts to stand on end, you are in an area where lightning will strike shortly.
You should IMMEDIATELY move to some type of enclosed shelter preferably a building or your vehicle.
FLASH FLOODING
- Remember “Turn Around, Don’t Drown”
- When heavy rain threatens, get out of areas subject to flooding. This includes creeks, streams, dips, washes low spots,
canyons as well as low water crossings.
- Don’t camp or park vehicles along streams and creeks, particularly during threatening weather.
- Avoid already flooded and high velocity flow areas. Do not cross, on foot or in your vehicle, quickly flowing creeks, streams
or low water crossings especially if you don’t know water depth.
- Road beds may not be intact in low water crossings during flash flood episodes. Be especially cautious at night when it is
harder to recognize flood dangers.
- If your vehicle stalls in high water, LEAVE IT IMMEDIATELY AND SEEK HIGH GROUND.
TORNADOES
- When tornadoes threaten, you should leave automobiles and mobile homes for more substantial shelter.
- In substantial shelter, you should put as many walls between you and the tornado as you can. This means that interior
bathrooms, hallways and closets on the lowest floor are the best place to be. If it is available, move to a below ground
shelter, such as a basement.
- Stay away from windows.
- Do not try to outrun a tornado in your automobile.
- If caught outside or in a vehicle with an approaching tornado, lie flat in a nearby ditch or depression (away from your
vehicle if you’re leaving it).
HURRICANES
- Even though we are more than 100 miles inland from the coast, landfalling hurricanes can still be a serious threat locally.
- High winds, even hurricane force winds, can occur locally.
- Torrential rains can cause severe flash and river flooding.
- Sudden, quick moving tornadoes are common with landfalling hurricanes.. even hundreds of miles inland.
- Evacuees from coastal areas will move inland into our area. Roadways may become congested along with a corresponding
shortage of hotel and other living spaces. Shelters may be set up throughout our area.
WINTER (COLD) WEATHER
- Bundle up when going out. Remember that most of the body heat that is lost to the atmosphere is lost from the region around
your head. Wear caps or hats keeping as much of your head (ears, etc) covered as possible.
- Even though air temperatures must be below 15 degrees F with wind speeds in excess of 25 to 30 mph to achieve wind chill
temperatures of -25 degrees F or lower, if that does occur, the human body becomes incapable of matching the rate of heat
loss. As a result, with wind chill temperatures of -25 degrees F or below, skin temperatures will decrease and exposed flesh
may freeze.
- In freezing and frozen precipitation, driving conditions are dangerous. On roadways, slow down (even if other motorists
don’t!). When stopping, don’t lock your brakes. Touch them, slowing the vehicle gradually. If the wheels lock, take your
foot off of the brakes. If you start skidding, steer the car in the direction that you want to go.
SUMMER (HEAT) WEATHER
- When the temperatures go up, you should slow down!
- Heed your body’s early warnings. Reduce your activities and stay in a shady, cool or air conditioned place as much as
possible.. especially when relative humidity levels are high.
- Don’t dry out. Drink plenty of non-alcoholic liquids while the hot spell lasts. Doctors recommend a glucose replacement drink
for those outdoors for more than an hour or two. If this is not available, a good substitute is plain water.
- Dress for hot weather. Wear lightweight, light colored and loose fitting clothing to help maintain normal body temperatures.
A hat or cap, and sunglasses are a must if prolonged exposure to the sun’s rays and glare is anticipated.
- Avoid thermal shock. Go slow for those first few real hot days. Heatstroke frequently develops swiftly with little warning.
Heatstroke is imminent if you quit sweating, which is your body’s air conditioning system. Immediate medical attention
is necessary with heat related illnesses.
© 2015 - Troy M. Kimmel, Jr. (email: [email protected]) / KimCo Meteorological Services
40
KOPPEN CLIMATE CLASSIFICATION
“A” CLIMATE TYPE - TROPICAL - All Months Have an Average Temperature of 18C/64F or Higher
Af - Tropical Rain Forest - Year Around Rainfall
All Months Have at least 2.4" of Rainfall
Aw - Tropical Wet and Dry (Savanna) - Winter Dry Season
At Least One Winter Month has Rainfall Less than 2.4"
As - Tropical Wet and Dry (Savanna) - Summer Dry Season
At Least One Summer Month has Rainfall Less than 2.4"
Most Rare Climate Type on Earth - Eastern Brazil Only
Am - Tropical Monsoon - Short Strongly Developed Dry Season
At Least One Month has Rainfall Less than 2.4"
“B” CLIMATE TYPE - ARID / SEMIARID - Potential Evaporation and Transpiration Exceed Precipitation (Moisture Deficit)
(Note: “B” Climates Cover 26% of Earth’s Land Surface Which is More Than Any Other Major Climate Type)
(BW - Arid -12% of Earth’s Land Area - Precipitation is Less than Half of Potential Evaporation/Transpiration)
BWh - Low Latitude (Hot) Desert Sinking Motion of Subtropical High - Average Annual Temp 18C/64F or Higher
BWk - Mid Latitude (Cold) Desert Land Locked Middle Latitude Deserts - Average Annual Temp <18C/64F
(BS - Semiarid -14% of Earth’s Land Area - Precipitation More Than Half But Still Less Than Potential Evap/Transpiration)
BSh - Steppe Grassland - Average Annual Temp is 18C/64F or Higher
BSk - Steppe Grassland - Average Annual Temp is <18C/64F
“C” CLIMATE TYPE - SUBTROPICAL - Avg Temp of Coldest Month of the Year is Below 18C/64F and Above -3C/27F
Cfa - Humid Subtropical - East Coast with Year Around Rainfall (****Austin is in this climate type****)
Average Temperature of the Warmest Month Above 22C/72F
At Least 4 Months with Average Monthly Temperature >10C/50F
Cwa - Humid Subtropical - Distinctly Dry Winter
Average Temperature of the Warmest Month > 22C/72F
At Least 4 Months with Average Monthly Temperature >10C/50F
Wettest Month of Summer Has At Least 10x the Precipitation of the Driest Month of Winter
Cfb - Marine West Coast - Wet Year Around
Average Temperature of All Months < 22C/72F; At Least 4 Months with Average > 10C/50F
Cfc - Marine West Coast - Wet Year Around
Average Temperature of All Months < 22C/72F; 1 to 3 Months with Average > 10C/50F
Csa - Mediterranean - Said to be One of the Most “Pleasant” Climates on Earth
Average Rainfall of Driest Summer Month <1.2"
Average Rainfall of Wettest Winter Month at Least 3x that of Driest Summer Month
Average Temperature of Warmest Month >22C/72F; At Least 4 Months with Average >10C/50F
Csb - Mediterranean - Said to be One of the Most “Pleasant” Climates on Earth
Average Rainfall of Driest Summer Month <1.2"
Average Rainfall of Wettest Winter Month at Least 3x that of Driest Summer Month
Average Temperature of Warmest Month <22C/72F; At Least 4 Months with Average >10C/50F
“D” CLIMATE TYPE - TEMPERATE - Avg Temp of Coldest Month of Year is -3C/27F or Below; Avg Temp Warmest Month >10C/50F
Dfa - Humid Continental - Hot Summers and Year Around Rainfall
Average Temperature of Warmest Month >22C/72F; At Least 4 Months with Average Monthly Temperature >10C/50F
Dwa - Humid Continental - Hot Summers and Dry Winter
Average Temperature of Warmest Month >22C/72F; At Least 4 Months with Average Monthly Temperature >10C/50F
Wettest Month of Summer Has At Least 10x the Precipitation of the Driest Month of Winter
Dfb - Humid Continental - Mild Summers and Year Around Rainfall
Average Temperature of All Months <22C/72F; At Least 4 Months with Average Monthly Temperature >10C/50F
Dwb - Humid Continental - Mild Summers and Dry Winter
Average Temperature of All Months <22C/72F; At Least 4 Months with Average Monthly Temperature >10C/50F
Wettest Month of Summer Has At Least 10x the Precipitation of the Driest Month of Winter
Dfc - Subarctic - Cool Summer and Year Around Rainfall
Average Temperature of All Months <22C/72F; Only 1 to 3 Months with Average Monthly Temperature >10C/50F
Dwc - Subarctic - Cool Summer and Dry Winter
Average Temperature of All Months <22C/72F; Only 1 to 3 Months with Average Monthly Temperature >10C/50F
Wettest Month of Summer Has At Least 10x the Precipitation of the Driest Month of Winter
Dfd - Subarctic - Cold Summer and Year Around Rainfall
Average Temperature of Coldest Winter Month is -38C/-36F or Below (Severe Winters)
Average Temperature of Warmest Summer Month >10C/50F
Dwd - Subarctic - Cold Summer and Dry Winter
Average Temperature of Coldest Winter Month is -38C/-36F or Below (Severe Winters)
Average Temperature of Warmest Summer Month >10C/50F
Wettest Month of Summer Has At Least 10x the Precipitation of the Driest Month of Winter
“E” CLIMATE TYPE - POLAR - Avg Temp of the Warmest Month <50F
ET - Tundra Climate Average Temperature of the Warmest Month of the Year is >0C/32F but <10C/50F
EF - Ice Cap Climate Average Temperature of the Warmest Month of the Year is 0C/32F or Below
“H” CLIMATE TYPE - HIGHLAND/MOUNTAINS
H - Highland Climate Very Complex and Tight Knit - Controlling Factors: Elevation and Exposure
41
WEATHERGRAPH Observation and Plotting
TIME ZONES
This chart shows how to convert a
UTC hour to a local hour.
Eastern :
Central:
Mountain:
Pacific:
HAILSTONE SIZES
Size
1/4”
1/2”
3/4”
1”
1 1/4”
1 1/2”
1 3/4”
2”
2 1/2”
2 3/4”
3”
4”
4 1/2”
Equivalent
Pea
Marble
Dime
Quarter
Half Dollar
Walnut
Golfball
Hen Egg
Tennis Ball
Baseball
Tea Cup
Grapefruit
Softball
Freefall
Velocity
25 mph
35 mph
43 mph
50 mph
56 mph
61 mph
66 mph
72 mph
80 mph
85 mph
89 mph
106 mph
117 mph
Freefall
Energy
0.02 ft-lbs
0.09 ft-lbs
0.44 ft-lbs
1.43 ft-lbs
3.53 ft-lbs
7.35 ft-lbs
13.56 ft-lbs
23.71 ft-lbs
57.48 ft-lbs
85.95 ft-lbs
122.66 ft-lbs
413.31 ft-lbs
724.85 ft-lbs
subtract 5 (4 for daylight saving)
subtract 6 (5 for daylight saving)
subtract 7 (6 for daylight saving)
subtract 8 (7 for daylight saving)
FUJITA SCALE
F0: 40-72 mph. Twigs and
branches snap off trees. Some
windows break.
F1: 73-112 mph. Pushes moving
cars off road. Flips mobile homes.
F2: 113-157 mph. Uproots large
trees and rips roofs off frame
houses.
F3: 158-206 mph. Severe damage.
Cars lifted and thrown. Trains
overturned.
F4: 207-260 mph. Levels well-built
homes.
F5: 261-318 mph. Incredible
damage. Foundations swept clean.
BEAUFORT WIND SCALE
No
0
1
2
3
Mph
0-1
1-3
4-7
8-12
Kts
0-1
1-3
4-6
7-10
4
5
6
7
8
9
13-18
19-24
25-31
32-38
39-46
47-54
11-16
17-21
22-27
28-33
34-40
41-47
10
55-63
48-55
Description
Smoke rises vertically
Wind moves smoke but not wind vanes
Wind felt on face; leaves rustle; wind vane moved
Leaves and small twigs in constant motion; wind extends
light flag
Dust and loose paper raised; small branches moved
Small trees with leaves begin to sway
Large branches in motion; whistling in telephone wires
Whole trees in motion; resistance felt walking against wind
Twigs broken off trees; wind generally impedes progress
Slight structural damage occurs (chimney pots and slate
removed)
Trees uprooted
METAR OBSERVATION FORMAT
KLEX 162354Z 20004KT 1 1/2SM -RA BR FEW004 BKN030
OVC050 22/21 A3006 RMK AO2 RAE05B34 SLP173 P0002
60007 70112 T02221011 51006=
KLEX, Lexington, Kentucky; 16th day of month; 2354 UTC; wind from 200 deg at 04
knots; visibility 1 1/2 statute mile in light rain and fog; few clouds at 400 ft; broken layer at
3000 ft; overcast layer at 5000 ft; temperature 22 deg C; dewpoint 21 deg C; altimeter
setting (pressure) 30.06 inches; A02 (automated station, type 2 which reports precip);
rain ended at 05 minutes past hour and began at 34 minutes past hour; sea level
pressure 1017.3 mb; 0.02” of precip in past hour; 0.07” of precip in past 6 hours; 1.12” in
past 12 hours; exact temp 22.2 deg C; exact dewpoint -1.1 deg C; pressure rising by 0.06
mb.
SYNOPTIC OBSERVATION FORMAT
68842 11682 72516 10176 20145 30126 40199 51010
69903 72052 875// 555 91020=
Port Elizabeth, South Africa (68842); precipitation data will be included (1); station type is
manned and weather is included (1); lowest cloud height is 1000 to 1500m above ground
(6); visibility is 40 km (82); sky cover 7/8ths (7); wind direction 250 deg (250); wind speed
16 kt (16); temperature 17.6 deg C (10176); dewpoint 14.5 deg C (20145); station
pressure is 1012.6 mb (0126); sea level pressure 1019.9 mb (0199); pressure tendency
rising then steady (1) changing by 1.0 mb (10); precipitation amount is trace (990) over a
time period of 18 hours (3); weather is recent drizzle (20); previous weather had been
drizzle (5) and clouds covering more than half of sky (2); low or middle cloud amount is 7/
8ths (7); low cloud is stratocumulus (5); middle cloud is not visible (/); high cloud is not
visible (/). Everything after the triple-digit group consists of regionally-defined data
groups.
DIGITAL ATMOSPHERE
The premier software package for detailed weather analysis. Unlimited 30-day trial!
www.weathergraphics.com/da
MPH =
COLD FRONT
OCCLUDED FRONT
COLD FRONTOGENESIS
STATIONARY FRONT
COLD FRONTOLYSIS
TROUGH
Knots =
m/s =
Deg F =
RIDGE
WARM FRONT
A scale of tornado damage.
CONVERSIONS
Deg C =
DRYLINE
WARM FRONTOGENESIS
HIGH PRESSURE
CENTER
WARM FRONTOLYSIS
MISCELLANEOUS SYMBOLS
H
LOW PRESSURE
CENTER
L
The numbers pertain to code representations
used in transmitted reports, and the
pictograms are used as part of a station plot.
Deg K =
mb =
inches =
TOTAL SKY COVER — 6/8
TEMPERATURE — 80°F
WEATHER — Heavy rain
VISIBILITY — 1 statute mile
DEWPOINT — 63°F
knots x 1.15
m/s x 2.2356
MPH x 0.8696
m/s x 1.944
knots x 0.5144
MPH x 0.4473
( Deg C x 1.8 ) + 32
( ( Deg K - 273.16 ) x 1.8 ) + 32
( Deg F - 32 ) x 0.555
Deg K - 273.16
Deg C + 273.16
( ( Deg F - 32 ) x 0.555 ) + 273.16
inches x 33.8636
mb x 0.029530233
1
LOW CLOUD — stratus
LOW CLOUD COVER — 3/8
LOW CLOUD HEIGHT — 300-599 ft
HIGH CLOUD — cirrus
MIDDLE CLOUD — altocumulus
WIND DIRECTION — from NE
WIND SPEED — 25 mph
PRESSURE — 1012.3 mb
PRESSURE CHANGE — 0.7 mb
PRESSURE CHANGE — falling then rising
PAST WEATHER — showers
PRECIP TIME — 3-4 hours ago
6-HR PRECIP — 0.12 inches
80
123
7
3 4
63
2 .12
SURFACE STATION PLOT
Numbers indicate the weather code as used in synoptic weather
reports (ww, present weather reported from a manned weather
station, as defined in WMO Pub. No. 306-A).
N Total sky cover
a Pressure trend
W Past weather
CL Low cloud
CM Middle cloud
CH High cloud
WEATHER SYMBOLS
0
0
0
0
0
0
00
01
02
03
04
05
06
07
08
09
No clouds.
Rising then falling.
Cloud covering half or
less of sky throughout
period.
No low clouds.
No middle clouds.
No high clouds.
Cloud development not
observed/observable
during past hour.
Clouds generally
dissolving during past
hour.
State of sky unchanged
during past hour.
Clouds generally forming
or developing during past
hour.
Visibility reduced by
smoke.
Haze.
Dust suspended in the
air, but not raised by
wind.
Dust or sand raised by
wind.
Dust devils now or within
past hour.
Duststorm or sandstorm
not at station but within
sight.
1
1
1
L1
M1
H1
10
11
12
13
14
15
16
17
18
19
1/8, or 1 tenth cloud
cover.
Rising, then steady; or
rising, then rising more
slowly.
Cloud covering both
more than half and less
than half of sky during
period.
CUMULUS, with little
vertical development and
seemingly flattened.
ALTOSTRATUS,
CIRRUS, in the form of
semitransparent, thin
filaments or hooks, not
enough to see sun/moon. invading the sky.
Mist.
Patches of shallow fog at Continuous shallow fog
station, not deeper than 2 at station, not deeper
m (10 m at sea).
than 2 m (10 m at sea).
Lightning visible, but no
thunder heard.
Precipitation visible but
not reaching ground at
station.
Precipitation reaching the Precipitation reaching the Thunder heard but no
ground not at or near the ground not at the station precipitation at the
station but at a distance. but nearby.
station.
Wind squall now or
during the past hour.
Tornado, waterspout, or
funnel cloud observed
now or during past hour.
2
2
2
L2
M2
H2
20
21
22
23
24
25
26
27
28
29
Cloud covering more
than half of sky
throughout period.
CUMULUS, of
considerable size.
Towering cumulus.
ALTOSTRATUS or
NIMBOSTRATUS. The
sun/moon can’t be seen.
CIRRUS, dense, and in
patches/twisted sheaves,
not invading sky.
Recent drizzle (not
freezing, not showers)
during past hour.
Recent rain (not freezing,
not showers) during past
hour.
Recent snow (not
showers) during past
hour.
Recent rain and snow
Freezing drizzle or rain
(not showers) during past (not showers), not now
hour.
but during past hour.
Rain showers, not now
but during past hour.
Snow showers, not now
but during past hour.
Hail or hail and rain, not
now but during past hour.
Fog, not now but during
past hour.
Thunderstorm, with or
without precipitation, not
now but during past hour.
3
L3
M3
H3
30
31
32
33
34
35
36
37
38
39
CUMULONIMBUS, tops
are not fibrous, cirriform,
or anvil-shaped.
ALTOCUMULUS, at
single level, and
semitransparent.
CIRRUS, often anvilshaped and associated
with cumulonimbus.
Slight/moderate
duststorm or sandstorm,
decreased during hour.
Slight/moderate
duststorm or sandstorm,
no change during hour.
Slight/moderate
duststorm or sandstorm,
increased during hour.
Severe duststorm or
sandstorm, which has
decreased during hour.
Severe duststorm or
sandstorm, no change
during past hour.
Duststorm or sandstorm,
severe, has increased
during past hour.
Drifting snow, slight or
moderate.
Drifting snow, heavy.
Blowing snow, slight or
moderate.
Blowing snow, heavy.
2/8, or 2 to 3 tenths cloud Rising, steadily or
cover.
unsteadily.
3
3
3/8, or 4 tenths cloud
cover.
Falling or steady, then
Sandstorm, or duststorm,
rising; or rising then rising or drifting or blowing
more rapidly.
snow.
4
4
4
L4
M4
H4
40
41
42
43
44
45
46
47
48
49
4/8, or 5 tenths cloud
cover.
Steady.
Fog or thick haze.
STRATOCUMULUS,
formed by the spreading
out of cumulus.
ALTOCUMULUS, in
patches, continuously
changing.
CIRRUS, in the form of
hooks or filaments,
invading the sky.
Fog at a distance but not
at station during past
hour.
Patchy fog.
Fog, sky discernable,
and has become thinner
during past hour.
Fog, sky not discernable,
and has become thinner
during past hour.
Fog, sky discernable, no
change during past hour.
Fog, sky not visible, no
change during past hour.
Fog, sky visible, has
begun or become thicker
during past hour.
Fog, sky not visible, has
begun or become thicker
during past hour.
Freezing fog, sky visible.
Freezing fog, sky not
visible.
5
5
5
L5
M5
H5
50
51
52
53
54
55
56
57
58
59
5/8, or 6 tenths cloud
cover.
Falling, then rising.
Drizzle.
STRATOCUMULUS, not
formed by the spreading
out of cumulus.
ALTOCUMULUS,
invading sky and usually
thickening.
CIRRUS or CIRROSTRATUS, invading sky,
bulk not 45° above horizon.
Drizzle, light, intermittent, Drizzle, light, continous,
not freezing.
not freezing.
Drizzle, moderate,
intermittent, not freezing.
Drizzle, moderate,
continuous, not freezing.
Drizzle, heavy,
intermittent, not freezing.
Drizzle, heavy, continous, Freezing drizzle, light.
not freezing.
Freezing drizzle,
moderate or heavy.
Drizzle and rain mixed,
light.
Drizzle and rain mixed,
moderate or heavy.
6
6
6
L6
M6
H6
60
61
62
63
64
65
66
67
68
69
Rain.
STRATUS, in continous
layer or shreds. No
stratus of bad weather.
ALTOCUMULUS, formed
by spreading out of
cumulus.
CIRRUS or CIRROSTRATUS, invading sky,
bulk 45° or more above
horizon.
Rain, light, intermittent,
not freezing.
Rain, light, continous, not Rain, moderate,
freezing.
intermittent, not freezing.
Rain, moderate,
continuous, not freezing.
Rain, heavy, intermittent,
not freezing.
Rain, heavy, continous,
not freezing.
Freezing rain, light.
Freezing rain, moderate
or heavy.
Rain and snow mixed,
light.
Rain and snow mixed,
moderate or heavy.
H7
70
71
72
73
74
75
76
77
78
79
Falling, then steady; or
6/8, or 7 to 8 tenths cloud falling, then falling more
slowly.
cover.
7
7
7
L7
M7
7/8, or 9 tenths cloud
cover.
Falling, steadily or
unsteadily.
Snow.
STRATUS, of bad
weather (scud), and often
with nimbostratus.
ALTOCUMULUS, not
invading sky, usually
double-layered/opaque.
CIRROSTRATUS,
completely covering the
sky.
Snow, light, intermittent.
Snow, light, continous.
Snow, moderate,
intermittent.
Snow, moderate,
continous.
Snow, heavy, intermittent. Snow, heavy, continous.
Ice needles, with or
without fog.
Snow grains, with or
without fog.
Snow crystals, with or
without fog.
Ice pellets (sleet).
8
8
8
L8
M8
H8
80
81
82
83
84
85
86
87
88
89
Sky completely covered
with clouds.
Steady or rising, then
falling; or falling, then
falling more rapidly.
Showers.
STRATOCUMULUS and
CUMULUS with bases at
different levels and not
formed by spreading Cu.
ALTOCUMULUS, in the
form of cumuliform tufts
(castellanus).
CIRROSTRATUS, not
invading the sky and not
completely covering sky.
Rain showers, light.
Rain showers, moderate
or heavy.
Rain showers, torrential.
Rain/snow showers
mixed, light.
Rain/snow showers
mixed, moderate or
heavy.
Snow showers, light.
Snow showers, moderate Ice pellet showers, light.
or heavy.
Ice pellet showers,
moderate or heavy.
Hail, light, not associated
with thunder.
9
9
9
L9
M9
H9
90
91
92
93
94
95
96
97
98
99
Thunderstorm, with or
without precipitation.
CUMULONIMBUS,
whose tops are clearly
fibrous or anvil-shaped.
ALTOCUMULUS, at
many layers (a chaotic
sky).
CIRROCUMULUS
predominating all other
cirriform clouds.
Hail, moderate or heavy,
not associated with
thunder.
Rain, light. Thunder
heard during past hour
but not now.
Rain, moderate or heavy.
Thunder heard during
past hour but not now.
Light snow or rain/snow
mixed with hail. Thunder
heard during past hour.
Moderate or heavy snow
or rain/snow with hail.
Thunder in past hour.
Thunderstorm, light or
moderate. Rain or snow,
but no hail.
Thunderstorm, light or
moderate, with hail.
Thunderstorm, severe.
Rain or snow, but no hail.
Thunderstorm, with
duststorm or sandstorm.
Thunderstorm, severe,
with hail.
Sky obscured (clouds not
visible due to rain, snow,
fog, or other obscuration).
NOT USED
Revision 3 This chart may be reproduced for personal use. Regarding distribution activities, such as offering this file on your website, or printing copies for use by schools, universities, and agencies, we grant
42 reserved.
permission providing we receive prior notification at [email protected] . All other use, including resale, is strictly prohibited without secured written permission from us. All rights
Copyright ©1998 WEATHER GRAPHICS TECHNOLOGIES, P.O. Box 450211, Garland TX 75045 www.weathergraphics.com
WEATHER SYSTEM CATEGORIES
WEATHERGRAPH Forecasting
Planetary scale
Synoptic scale
Mesoscale
Microscale
10,000 + km
General atmospheric circulation
1,000 - 10,000 km Frontal systems, synoptic highs and lows
10 - 1,000 km
Thunderstorms, tropical cyclones
1 - 10 km
Clouds, tornadoes, mountain waves
TROPICAL SYSTEMS
Classification
Sustained wind speed
Knots
MPH
TROPICAL DISTURBANCE
33 or less
38 or less
TROPICAL DEPRESSION*
33 or less
38 or less
TROPICAL STORM
34-63
39-73
HURRICANE/TYPHOON
64 or more
74 or more
MAJOR HURRICANE**
96 or more
110 or more
SUPERTYPHOON* *
130 or more
149 or more
* Has a closed circulation ** Designation is nonstandard or may apply regionally
TROPICAL CYCLONE REQUIREMENTS
— Sea surface temperatures in excess of 80 deg F over large open ocean areas.
— Coriolis effect, equal to that at 5 degrees latitude or greater
— Weak vertical wind shear; preferably below 20 kts shear from 850 to 200 mb
EASTERLY WAVES
A migratory disturbance in the tropical easterlies that moves westward. They are
most common in the Atlantic basin and may evolve into tropical cyclones. Easterly
waves are usually stable but may be one of the following:
Wave type
Precipitation
Slope w/ height
Wnd spd w/ height
Stable
West of wave
Eastward
Decreases
Neutral
At wave
Little if any
Little change
Unstable
East of wave
Westward
Increases
SAFFIR-SIMPSON HURRICANE SCALE
Cat 1 — Minimal damage
Pressure >980 mb (>28.92”); winds 74-95 mph; storm surge 4-5 ft.
Damage primarily to shrubbery, trees, foliage, and unanchored mobile homes. No real
damage to other structures. Some damage to poorly-constructed signs. Low-lying
coastal roads inundated, minor pier damage, some small craft torn from moorings in
exposed anchorage.
Cat 2 — Moderate damage
Pressure 965-979 mb (28.49-28.92”); winds 96-110 mph; storm surge 6-8 ft.
Considerable damage to shrubbery and tree foliage; some trees blown down. Major
damage to exposed mobile homes. Extensive damage to poorly-constructed signs.
Some damage to roofing materials on buildings; some window and door damage. No
major damage to buildings. Coastal roads and low-lying escape routes are cut by
rising water two to four hours before the arrival of the storm. Considerable damage to
piers. Small craft torn from mooring.
Cat 3 — Extensive damage
Pressure 945-964 mb (27.90-28.48”); winds 111-130 mph; storm surge 9-12 ft.
Foliage torn from trees. Large trees and signs blown down. Some structural damage
to small buildings. Mobile homes destroyed. Serious flooding at coast. Large
structures near coast damaged by battering waves and floating debris. Low-lying
escape routes cut by rising water three to five hours before storm arrives.
Cat 4 — Extreme damage
Pressure 920-944 mb (27.17-27.89”); winds 131-155 mph; storm surge 13-18 ft.
Numerous trees blown down. Extensive damage to roofing materials. Complete
failure of roofs on many small residences. Flat terrain is submerged ten feet or less
above sea level as far as six miles inland. Major damage to lower floors of structures
near shore due to battering by waves and floating debris. Major erosion of beaches.
Cat 5 — Catastrophic damage
Pressure <920 mb (<27.17”); winds >155 mph; storm surge >18 ft.
Considerable damage to buildings. Major damage to lower floors of all coastal
structures less than 15 feet above sea level and within 500 yards of shore.
TURBULENCE
Using the 300, 250, and
200 mb charts, some
favored areas for clear air
turbulence are:
* Regions just poleward of
the jet stream
* Horizontal wind shear of
40+ kts per 150 nm
* Vertical wind shear of 6+
kts per 1000 ft
* Temperature gradient of
5+ deg C per 120 nm
* Winds of 135+ kts in
strong anticyclonic flow
Type of system
Cold barotropic low
Surface
Indication
Low
Upper Air
Indication
Deep low
Warm barotropic low
Low
Weak high
Cold barotropic high
Warm barotropic high
Baroclinic low
Baroclinic high
High
High
Low
High
Weak low
Strong high
Wave
Wave
STABILITY INDICES
Types of system
Decaying frontal wave
Cutoff low
Heat low
Tropical cyclone*
Arctic high
Subtropical high
Frontal low
Migratory high
* High is usually only discernable at 300 mb or above.
HEAVY SNOW FORECASTING
With major frontal systems, the heaviest snow usually falls in a band between 50 nm and 200 nm to the left
of the surface low’s track. Heavy snowfall tends to diminish with passage of the 700 mb low.
PROGGING RULES
q A major short wave trough moving A into B out of a long wave trough A deepens B fills the long wave trough.
q A major short wave ridge moving A into B out of a long wave ridge A builds B weakens the long wave ridge.
q A jet streak moving A toward B through C away from the axis of a long wave trough will cause it to A deepen and remain quasistationary B progress C fill and progress more rapidly.
q A jet streak moving A toward B through C away from the axis of a long wave ridge will cause it to A build and remain quasistationary B progress C weaken and progress more rapidly.
q An upper trough oriented NW-SE has negative tilt and tends to deepen; one oriented NE-SW has positive tilt and tends to fill.
q The stronger the westerly component of the upper-level wind, the faster the wave moves.
q Cold air advection deepens upper-level troughs and weakens upper-level ridges.
q Warm air advection builds upper-level ridges and fills upper-level troughs.
q Moisture in a parcel may increase due to these factors: upper divergence, warm air advection, frontal lift, orographic lift, boundarylayer convergence, colder air moving over a warmer surface, advection over a new moisture source, and on-shore flow.
q Moisture in a parcel may decrease due to these factors: upper convergence, cold air advection, adiabatic drying, warm air moving
over a cold surface, and offshore flow.
q Cold fronts will move at roughly 85% of the 850 mb flow in the cold air behind the cold front.
q Warm fronts will move at roughly 70% of the 850 mb flow in the cold air ahead of the warm front.
q Dynamic lows tend to have a surface motion of 70% of the 700 mb flow or 50% of the 500 mb flow.
FORECAST MODEL OVERVIEW
Name
LFM
LFM II
NGM
GSM
ETA
ETA
ETA
ETA
RUC1
RUC2
Forecast Model
Full Name
Limited-area Fine Mesh
Limited-area Fine Mesh
Nested Grid Model
Global Spectral Model
Eta (greek letter)
Eta (greek letter)
Eta (greek letter)
Mesoscale Eta
Rapid Update Cycle
Rapid Update Cycle
Domain
N. Amer.
N. Amer.
N. Amer.
Global
N. Amer.
N. Amer.
N. Amer.
U.S./Can
U.S.
N. Amer.
Type
Grid
Grid
Grid
Spectral
Grid
Grid
Grid
Grid
Grid
Grid
Grid Size
53 x 57
53 x 45
Nested
126 waves
N/A
N/A
N/A
N/A
81x62
151x113
Horz
Vert NWS
Resolutn Lyrs Implem Notes
190 km 7
1971
Discontinued
127 km 16 1977
Discontinued
90 km
16 1985
100 km 28 1980
Is also AVN (to 72h) and MRF (to 360h)
80 km
38 1993
48 km
38 1995
32 km
45 —
Experimental
29 km
50 —
Experimental
60 km
25 1994
Discontinued
40 km
40 1998
Model is assimilated every hour
WINTER PRECIPITATION GUIDELINES
<300’ thick
1200 ft AGL
Above 0 deg C
600 ft thick or more
Below 0 deg C
800 ft AGL
Rain
Rain/snow mix
Snow
Ice pellets (sleet)
Freezing rain
These are only guidelines for typical situations. Layer humidity and other factors will affect these rules and must be taken into account.
Revision 3 This chart may be reproduced for personal use. Regarding distribution activities, such as offering this file on your website, or printing copies for use by schools, universities, and agencies, we grant
43 reserved.
permission providing we receive prior notification at [email protected] . All other use, including resale, is strictly prohibited without secured written permission from us. All rights
KI — K Index, deg C
KI = T850 + Td 850 - T700 + Td 700 - T 500
0-15
0% chance of tstms
18-19
20% chance of tstms
20-25
35% chance of tstms
26-30
50% chance of tstms
31-35
85% chance of tstms
40+
100% chance of tstms
LI — Lifted Index, deg C
LI = Te500 - Tp500
Te = environment
>0
Thunderstorms unlikely
0 to -2
Thunderstorms possible
-3 to -5 Thunderstorms probable
< -5
Strong thunderstorm potential
Tp = lifted parcel
TI — Thompson Index, deg C
TI = KI - LI
<25
Thunderstorms unlikely
25-34
Slight chance of tstms
35-39
Few, widely, or scattered tstms
>40
Severe thunderstorms
SWEAT Index, dimensionless
<272
Thunderstorms unlikely
273-299 Slight risk of severe. General thunderstorms.
300-399 Moderate risk of severe. Approaching severe limits.
400-599 Strong risk of severe. Few thunderstorms. Isolated tornadoes.
600-799 High risk of severe. Scattered tornadoes.
>800
Possibly unconducive to tstms but wind damage possible.
EHI — Energy-Helicity Index, dimensionless
EHI = ( Positive SRH (0-2 km) x CAPE ) / 160000
0-2.0
Significant mesocyclone-induced tornadoes unlikely
2.0-2.4 Mesocyclone-induced tornadoes possible (F0-F1 damage)
2.5-2.9 Mesocyclone-induced tornadoes more likely.
3.0-3.9 Strong tornadoes suggested.
4.0+
Violent tornadoes suggested.
CAPE — Convective Availability of Potential Energy; B+ — Positive Energy, j/kg
300-1000
Weak severe potential
1000-2500
Moderate severe potential
2500-3000
Strong severe potential
BRN — Bulk Richardson Number, dimensionless
BRN = CAPE / BRN Shear
<10
Thunderstorms unlikely
11-49
Moderate potential for storms. Supercells possible.
>50
Strong potential for storms. Multicells possible.
SRH — Storm Relative Helicity, (m/s)2
150-299 Weak possibility of rotating storms
300-449 Moderate potential of rotating storms
>450
Strong possibility of rotating storms
1200 ft thick or more
600 ft AGL
VT — Vertical Totals Index; CT — Cross Totals Index); TT — Total Totals Index, deg C
VT = T 850 - T 500
CT = Td 850 - T500
TT = T d850 + T850 - ( 2 x T500)
VT
CT
TT
Indication
<25
<17
<43
Thunderstorms unlikely
18-19
44
Isold-few tstms
26
20-21
46
Sct tstms
22-23
48
Sct tstms, isold severe
30
24-25
50
Sct tstms, few severe, isold tornadoes
32
26-29
52
Sct-numerous tstms, few-sct severe, few tornadoes
>34
>30
56
Numerous tstms, sct severe, sct tornadoes
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Copyright ©1998 WEATHER GRAPHICS TECHNOLOGIES, P.O. Box 450211, Garland TX 75045 www.weathergraphics.com