Download Operational Tephigram Analysis File

Tephigram Analysis
All ASL
My printing from 1985 ….
Freezing Level
AMS FRLVL
 Not freezing
temperatures from
surface radiative
cooling

Above Freezing Layer - AFL
Near Freezing Layers - NFL
>30 mb thick
 -2oC to +1oC

Air Mass Analysis - The w plot
w conservative
property of air
masses
 w near the
surface influenced
by diabatic effects

Representative w in dry air
mass

Dry air
influences
on Tw
Cloud Analysis – Cloud Base

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Td increase or T-Td
Spread decrease
allow for hygristor and
thermistor lag
convective or turbulent
mixing occur base where
the narrowing spread
suddenly remains
constant, indicating a
saturated air mass (or
nearly)
ASL
Cloud Analysis – Cloud Top

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Td decrease or T-Td Spread
increase
allow for hygristor and thermistor
lag
super adiabatic lapse rate exists
due to evaporated cooling on the
sensor, the cloud top is located at
the start of the increasing spread.
convective clouds, the cloud tops
may be estimated by balancing
energies along the updraft curve.
The average convective cloud tops
will be at the equilibrium level (E).
The maximum cloud tops will reach
the energy balance level (EBL)
Cloud top heights can be derived
from satellite imagery by matching
the infrared temperature to a
representative tephigram
ASL
Cloud Amounts

Dewpoint Depressions
0 - 2C suggests overcast
2 - 4C suggests broken
4 - 6C suggests scattered

Suggested dewpoint depression ranges
should be increased with height at
temperatures below -12C (Frost Point
considerations - use 1C per 3000 feet
which corresponds to the moist adiabatic
lapse rate).
Cloud Types


Non-convective
Clouds–
stable
layers
Convective Clouds
Convective Cloud

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Convective Cloud BASE - LFC
Average TOPS - Equilibrium level E
Maximum TOPS - Energy Balance
Level EBL
Type - CU, TCU, ACC, CB, depends
on depth, strength, and level
Amount - SUBJECTIVE. The easier
it is to reach the LFC, the more
convection there will be.
Timing or Location - e.g. “Over and
in lee GRTLKS”, “mid-afternoon”,
etc.
TC - Surface temperature needed
for parcels to convect freely.
PL/LI - it is important to mark down
"PI/LI" if it exists. The bases and
tops of PI/LI need not be plotted.
This is primarily a flag for possible
convection.
Mid Level Convection –
ACC/CB


ACC is used to
denote mid-level
convection. TCU is
used to denote
surface-forced
convection, even if
the cloud base is in
the mid-levels.
CBs can arise from
surface or mid-level
forces.
Tephigram Exercises
Hodographs



The speed and
direction of warm and
cold fronts
Differential
temperature
advection , changing
stability
Expected vertical
motion near fronts
VWS varies with the isobaric thermal gradient
Thermal Wind Vector and
Horizontal Temperature Gradient
Applies when winds are nearly geostrophic
 Not in PBL, strong VV, strong curvature

Height of the Gradient Wind
Level
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wind in the PBL is a
combination of:
gradient wind
(geostrophic + curvature)
friction effects and
horizontal temperature
gradient.
Friction produces a
characteristic veering and
increase of wind with
height known as the
Ekman spiral
Total Thermal Wind & Vertical Wind
Shear
VT is wind
vector
difference
from the
uppr to
the lower
levels
 VWS is
VT/Z

The Hodograph and the Top of the
PBL

Typically at the top of the PBL, the wind speed
increases sharply and the characteristic veering
with height ends
Horizontal Temperature
Advection

Cold advection
requires that
winds back with
height
Horizontal Temperature
Advection

Warm advection
requires that
winds veer with
height
Differential Temperature
Advection and Changes in
Vertical Stability

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Impacts on stability
trends
Vertical changes in
thermal advection
Greater VWS –
greater thermal
advections
Differential Temperature
Advection and Changes in
Vertical Stability
Backing over
Veering
 Cold Advection
over Warm
Advection
 Decreasing
Stability

Non-Frontal Inversions

shallow radiation inversion in continental
arctic air
Applied Hodographs
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Height of a frontal
surface, base of mixing
zone.
Orientation of frontal
zone.
Direction of frontal
motion.
Speed of a front.
Instantaneous changes in
vertical stability.
Vertical motion in the
warm air mass.
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Relative maximum in
VWS is the mixing zone
of a front
Gradients of temperature
and humidity are always
in the cold air
Top of VWS is top of
mixing layer
Warm air above top of
VWS layer – nil thermal
gradients in warm air and
nil VWS
Applied Hodographs

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
Height of a frontal
surface, base of mixing
zone.
Orientation of frontal
zone.
Direction of frontal
motion.
Speed of a front.
Instantaneous changes in
vertical stability.
Vertical motion in the
warm air mass.

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Isotherms in mixing zone
parallel the front
VT in mixing zone parallel
the front
VT magnitude proportional
to magnitude of the front
Applied Hodographs

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Height of a frontal
surface, base of mixing
zone.
Orientation of frontal
zone.
Direction of frontal
motion.
Speed of a front.
Instantaneous changes in
vertical stability.
Vertical motion in the
warm air mass.

VN is the normal from the
origin perpendicular to
the VWS associated with
the front
Applied Hodographs

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Height of a frontal
surface, base of mixing
zone.
Orientation of frontal
zone.
Direction of frontal
motion.
Speed of a front.
Instantaneous changes in
vertical stability.
Vertical motion in the
warm air mass.

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Speed of a front at the
level identified on a
hodograph will be the
magnitude of VN -the
normal from the origin
perpendicular to the VWS
associated with the front
instantaneous speed
valuable for short range
prognosis
excellent check for frontal
motion.
Applied Hodographs

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Height of a frontal
surface, base of mixing
zone.
Orientation of frontal
zone.
Direction of frontal
motion.
Speed of a front.
Instantaneous changes in
vertical stability.
Vertical motion in the
warm air mass.


Changes in VWS
intensity
Changes in VWS type
Applied Hodographs

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Height of a frontal
surface, base of mixing
zone.
Orientation of frontal
zone.
Direction of frontal
motion.
Speed of a front.
Instantaneous changes in
vertical stability.
Vertical motion in the
warm air mass.

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
basis for short-range
cloud forecasting
assume that the frontal
surface does not change
slope for a short period of
time.
the equation of continuity,
implies that horizontal
divergence must be
accompanied by vertical
motion.
Active (or Anabatic) Cold Front
Component
of wind in
the warm
air above
the mixing
level is less
that the
speed of
the front
Inactive or Katabatic Cold Front
Component
of wind in
the warm
air above
the mixing
level is
more that
the speed
of the front
Active (or Anabatic) Warm Front
Normal to Front
Component
of wind in
the warm
air above
the mixing
level is
more than
the speed
of the front
Inactive (or Katabatic) Warm
Front
Backing wind in the warm air relative to the frontal shear denotes an
active – anabatic front.
Veering wind in the warm air relative to the frontal shear denotes an
inactive – katabatic front.
Component
of wind in
the warm
air above
the mixing
level is
less than
the speed
of the front
Hodograph Analysis
Methodology
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Identify the Gradient Wind Level (Top of the PBL)
Identify the wind at the top of the PBL. (Useful for estimating the
surface wind).
Identify layers with relatively strong vertical wind shear. For each
layer, determine the:
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top (frontal surface) and base of the mixing zone
vertical wind shear (for turbulence forecasting)
orientation of the frontal zone
speed and direction of motion of the front
vertical motion in the warm air mass
Identify the changes in vertical stability that would result from the
differences in the vertical temperature advections.
Collaborate the results of the hodograph analysis with other data
such as tephigrams, upper air analyses, and satellite imagery.
Example of Hodograph Analysis
and Interpretation
Example of Hodograph Analysis
and Interpretation
•AB is the shear in the friction layer- veering and increase with height.
•The gradient wind level is 3,000 ft.
•BC very small vertical wind shear - likely occurs within an air mass.
•CD gives a vertical wind shear of 8 kt per 1000 ft - a relative maximum = a frontal
zone. Frontal surface at 10,000 ft with base of the mixing zone is at 7,000 ft
•Frontal surface oriented WNW-ESE - colder air northeast of the station.
•Front is stationary. (VN is zero).
•Wind in the warm air above the frontal surface represented by DE are the same as the
frontal speed, there is little vertical motion above the frontal surface.
•EF - shear in a frontal zone, since there is a relative maximum of 6 kt per 1,000 ft in the
14,000 to 18,000 ft layer. Frontal surface at 18,000 ft with base of the mixing zone is at
14,000 ft.
•Frontal surface oriented south-north with colder air to the west of the station.
•Cold front moving eastward (from 270 degrees) at around 10 kt.
•Wind in the warm air above the frontal surface increase with height indicates slight
subsidence in the warm air mass.
•With cold air advection between 14,000 and 18,000 ft above little advection at lower
levels, the vertical column of the atmosphere below 18,000 ft must show decreasing
vertical stability with time.
Horizontal Temperature
Advection
Actual temperature changes in the
atmosphere may arise from
 diabatic processes
 vertical motion or
 horizontal temperature advection

T  VN  VT / z

t
120
(C/hr)
V in kt and the vertical wind shear is expressed in kt per 1000 ft
Parcel convection and the four
stability classifications
Identifying latent instability
Potential (convection)
instability