Download Fire Weather - University of Florida

Lesson 2C - Weather
2C-1-S190-EP
Lesson Objectives
1. Describe the affect of temperature and relative
humidity has on wildland fire behavior.
2. Describe the affect of precipitation on wildland
fire behavior.
3. Describe the differences between a stable and
unstable atmosphere.
4. Describe general and local winds.
5. Describe critical fire weather conditions.
6. List the different types of fire weather forecasts
and outlooks available.
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Fire Weather
*Click on image to play video
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Air Temperature
The degree of hotness or
coldness of a substance.
An average of the thermal
energy of a group of
particles in a substance
(does not depend on # of
particles)
In weather we refer to
this as air temperature or
dry bulb temperature.
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Temperature is measured with a
thermometer
calibrated either to
the FAHRENHEIT scale
or the CELSIUS or centigrade scale.
What influences air temperature?
•Time of day
•Season
•Elevation
•Topography
•Latitude
•Weather systems
•Bodies of water
Why does air temperature matter in
wildland fires?
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Relative Humidity
For a given air temperature, relative humidity
(%) is the amount of moisture in the air divided
by the amount the air could hold when
saturated; usually expressed in percent.
•Ranges from 1-100%...what does 100% mean?
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Temperature and RH Relationships
3 grams
3 grams
3 grams of H2O
50ºF
100%
(saturated)
70ºF
50%
(unsaturated)
90ºF
25%
(unsaturated)
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Thermograph
Temperature and RH Relationship
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Relative Humidity
Temperature vs. RH (general) for a
given volume of air
A
Temp. = 60 F
RH = X
B
Temp. = 80 F
RH = X/2
Temperature
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So what?
• Think of the fire triangles…what does RH
affect?
– Does this differ between fine/large fuels?
• Why does this matter for wildland fire
suppression?
• Why does this matter for prescribed
burning?
– Small changes in RH that aren’t noticed can have
significant impacts
• What should you do on a fire?
• Monitoring = belt weather kit
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Precipitation
Precipitation is liquid or solid
water particles that originate
in the atmosphere, and
become large enough to fall to
the earth’s surface.
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Precipitation
Amount vs. Duration
• Fine Fuels
– gain and lose moisture
quickly
– react rapidly to precipitation
• Heavy Fuels
– gain and lose moisture
slowly
– react slowly to precipitation
• Duration vs. Amount
– Precipitation duration has
greater impact on fuel
moisture than precipitation
amount
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Atmospheric Stability
The degree to which vertical motion in the atmosphere is
ENHANCED or SUPPRESSED.
*Click on image to play video
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Stable Atmosphere
Stable atmosphere resists upward vertical motion
*Click on image to play video
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Stable Atmosphere
Visual Indicators
• Visual Indicators
– Clouds form in
layers
– Smoke drifts apart
after limited rise
– Poor visibility due
to smoke or haze
– Fog layers
– Steady winds
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Stable Atmosphere
Visual Indicator Examples
• Clouds form in
layers
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Stable Atmosphere
Visual Indicator Examples
• Smoke drifts apart
after limited rise
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Stable Atmosphere
Visual Indicator Examples
• Poor visibility
due to smoke or
haze
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Stable Atmosphere
Visual Indicator Examples
• Fog Layers
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Stable Atmosphere
Visual Indicator Examples
• Steady Winds
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Stable Atmosphere
Inversion
*Click on image to play video
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Stable Atmosphere
Inversion Types
• Four Inversion Types
–
–
–
–
Nighttime (Radiation)
Frontal
Marine
Subsidence
• Two most common
types
– Nighttime (Radiation)
– Subsidence
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Stable Atmosphere
Nighttime Inversion
*Click on image to play video
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Stable Atmosphere
Thermal Belt
• Thermal Belt
– Nighttime inversions in
mountainous regions
– The warm layer
typically found on the
middle third of the
slope
– Characterized by the
highest minimum
temperature and lowest
minimum RH
– Fire can be very active
within the thermal belt
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Stable Atmosphere
Subsidence Inversion
*Click on image to play video
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Stable Atmosphere
Subsidence Inversion Facts
• Subsidence Inversion
– May persist for several
days
– May reach the surface
further enhancing fire
activity
– Typically results in
• clear or cloudless skies
• above average
temperatures
• low relative humidity
• drying of fuels
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Unstable Atmosphere
Encouraging upward vertical motion
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Unstable Atmosphere
Visual Indicators
• Visual Indicators
– Clouds grow vertically
and smoke rises to
great heights
– Cumulus clouds
– Good visibility
– Gusty winds
– Dust devils and
firewhirls
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Unstable Atmosphere
Visual Indicator Examples
• Clouds grow
vertically and
smoke rises to
great heights
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Unstable Atmosphere
Visual Indicator Examples
• Cumulus Clouds
• Good Visibility
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Unstable Atmosphere
Visual Indicator Examples
• Gusty Winds
• Dust devils and
firewhirls
*Click on image to play video
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Winds
Horizontal movement of air
*Click on image to play video
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Winds
Wind’s Effect on Wildland Fire
• Wind impacts the fire environment by:
–
–
–
–
Increasing the supply of oxygen to the fire.
Determining the direction of fire spread.
Increasing the drying of the fuels.
Carrying sparks and firebrands ahead of the main fire causing
new spot fires.
– Bending flames, which results in the preheating of fuels ahead of
the fire.
– Influencing the amount of fuel consumed by affecting the
residence time of the flaming front of the fire. The stronger the
wind, the shorter the residence time and the less fuel is
consumed.
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General Winds
*Click on image to play video
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Local Winds
*Click on image to play video
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Local Winds
Slope Winds
• Upslope Winds
– A result of differential
heating and convective
processes along the slope
– Average speeds range from
3 to 8 mph
– Develop along east facing
slope first and south and
west facing slope by late
morning
• Downslope Winds
– Air along the slope cools
and sinks producing the
downslope wind
– Average speeds range from
2 to 5 mph
– Develop on east facing
aspects first and south and
west facing aspects after
sunset
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Local Winds
Valley Winds
• Upvalley Winds
– As the air warm, temperature
and pressure differences
within the valley or adjacent
valleys result in upvalley
wind flow.
– Strongest mid to late
afternoon.
– Average speeds range from
10 to 15 mph.
• Downvalley Winds
– As the valley loses solar
heating, the air in the valley
cools.
– The cool air drains
downvalley.
– Average downvalley wind
speeds range from 5 to 10
mph.
– Typically develop a few
hours after sunset.
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Local Winds
Sea/Land Breeze
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Sea Breeze
1998 Perry Fire
Sea breeze interacting with Perry fire. Fire activity
increases when sea breeze front penetrates fire.
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Used in Rx prescriptions
•
•
•
LVORI- Low Visibility Occurrence
Risk Index
“Smog” index- risk of low visibility
(vehicles)
Increases with RH, and low DI
– From operational experience,
one should be VERY CAUTIOUS
ABOUT BURNING if one of the
following situations occurs:
– When LVORI for a nighttime
forecast period is 8,9 or 10
– When ACTIVE SMOKE from
stumps logs, etc. is present
during the night
– When there is a roadway within
three miles of a burn site with
open fields, logging roads, or
open streams that can provide an
easy transit of the smoke from
the burn site to the roadway
Table 1: Low Visibility Occurrence Risk Index (LVORI)
LVORI Category Interpretation
1
Lowest proportion of accidents with smoke and/or fog reported (130 of
127,604 accidents, or just over 0.0010 accidents.)
2
Physical or statistical reasons for not including in category 1, but proportion
of accidents not significantly higher.
3
Higher proportion of accidents than category 1, by about 30% to 50%, but of
marginal significance (1%-5%).
4
Significantly higher than category 1, by a factor of 2.
5
Significantly higher than category 1, by a factor of 3 to 10.
6
Significantly higher than category 1, by a factor of 10 to 20.
7
Significantly higher than category 1, by a factor of 20 to 40.
8
Significantly higher than category 1, by a factor of 40 to 75.
9
Significantly higher than category 1, by a factor of 75 to 125.
10
Significantly higher than category 1, by a factor of 150.
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Used in Rx prescriptions
• Dispersion Index
– Estimates daytime and nightime stability of the
atmosphere. Higher DI = greater mixing, but very
high = potential fire control problems
– Doubling of the DI results in a doubling of the amount
of smoke the airshed can hold
– RX : 41-70
– Under 30, could be OK…if small unit with little smoke,
or stagnant if winds are low
– Over 71: very good dispersion…but hazardous to
burn
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Those who know
how to read and
heed weather!
Those who think they can
“weather it all”
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2008 burn
Winter Annual
ACMF
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Review Lesson Objectives
1. Describe the affect of temperature and relative
humidity has on wildland fire behavior.
2. Describe the affect of precipitation on wildland
fire behavior.
3. Describe the differences between a stable and
unstable atmosphere.
4. Describe general and local winds.
5. Describe critical fire weather conditions.
6. List the different types of fire weather forecasts
and outlooks available.
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Critical Fire Weather
*Click on image to play video
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Critical Fire Weather
Cold Fronts
*Click on image to play video
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Critical Fire Weather
Foehn Winds
*Click on image to play video
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•
•
•
•
•
•
•
•
•
•
Meteorology
Santa Ana winds are a type of drainage wind, an offshore wind that results from the buildup of air
pressure in the high-altitude Great Basin between the Sierra Nevada and the Rocky Mountains. When
upper level winds are favorable, this high altitude air mass spills out of the Great Basin and is propelled
gravitationally towards the southern California coastline, generally as a northeasterly wind.
It is often said that the air is heated and dried as it passes through the Mojave and Sonoran deserts, but
according to meteorologists this is a popular misconception. The Santa Ana winds usually form during
autumn and early spring when the surface air in the elevated regions of the Great Basin and Mojave
Desert (the "high desert") becomes cool or even cold, although they may form at virtually any time of
year. The air heats up due to adiabatic heating during its descent. While the air has already been dried
by orographic lift before reaching the Great Basin as well as by subsidence from the upper atmosphere,
the relative humidity of the air is further decreased as it descends from the high desert toward the coast,
often falling below 10 percent.
The air from the high desert is initially relatively dense owing to its coolness and aridity, and thus tends
to channel down the valleys and canyons in gusts which can attain hurricane force at times. As it
descends, the air not only becomes drier, but also warms adiabatically by compression. The southern
California coastal region gets some of its hottest weather of the year during autumn while Santa Ana
winds are blowing. During Santa Ana conditions it is typically hotter along the coast than in the deserts.
QuikSCAT image showing the speed of the Santa Ana winds (m/s).
Note that while the Santa Ana Winds are an adiabatic wind, they are not a Föhn wind. A Föhn wind
results from precipitation on the windward side of a mountain range which releases latent heat into the
atmosphere which is then warmer on the leeward side (e.g. the Chinook or the original Föhn). The
Santa Ana winds do not originate in precipitation, but in the bone-dry high deserts.
The combination of wind, heat, and dryness accompanying the Santa Ana winds turns the chaparral into
explosive fuel feeding the infamous wildfires for which the region is known. Wildfires fanned by Santa
Ana winds burned 721,791 acres (2,921 km²) in two weeks during October 2003.[1] These same winds
have contributed to the fires that have burned some 426,000 acres (1,720 km2) as of late October
2007.[2]
Although the winds often have a destructive nature, they have some positive benefits as well. They
cause cold water to rise from below the surface layer of the ocean, bringing with it many nutrients that
ultimately benefit local fisheries. As the winds blow over the ocean, sea surface temperatures drop
about 4°C (7°F), indicating the upwelling. Chlorophyll concentrations in the surface water go from
negligible, in the absence of winds, to very active at more than 1.5 milligrams per cubic meter in the
presence of the winds.
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Critical Fire Weather
Foehn Winds
• Common Foehn
Winds
– Chinook
– Wasatch
– North
– East
– Santa Ana
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San Diego, Oct. 2007Californias love
the Santa Ana winds
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Critical Fire Weather
Thunderstorms
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Critical Fire Weather
Dust Devils and Firewhirls
*Click on image to play video
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Complete Exercise 4
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Predictive Services
• Predictive Services
– Products Produce By:
• Agency Fire Meteorologists
• Intelligence Coordinator
• FBAN
• Fuels Specialists
– Monitors, analyzes and predicts
• Fire weather
• Fire danger
• Interagency fire management
resource impact
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Predictive Services (national, regional
websites)
• Predictive Services
– 7 Day Significant Fire
Potential
• Produced Weekly
• Daily in 2006
– 30 Day Fire Potential
• Produced Monthly
– Season Fire Potential
• Produced Annually
– Spring
– Fire Season Update
• Southern Area
Coordination Center
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DOF Website: http://www.fldof.com/fire_weather/forecast/seasonal_forecast.html
Seasonal Fire Weather Outlook: Updated January 4, 2008 January-March
2008
• Current Conditions Around Florida:
• The state began 2007 under neutral ENSO conditions but La Niña
conditions formed later in the year. Dry conditions persisted through the fall
due to the La Niña and positive Pacific North American (PNA)
pattern…According to the U.S. Drought Monitor, most of the state is
experiencing abnormally dry conditions with the south central part of the
state seeing moderate to severe drought conditions.
• Long-range Outlook:
• The outlook for the next three months is for the current La Niña pattern to
continue. Drought conditions are expected to worsen…Rainfall amounts are
forecast to be near average by June and above average toward the end of
the summer when we approach peak hurricane season.
Summary:
• Drought conditions are expected to worsen over the spring months as the
La Niña in the eastern Pacific Ocean persists. The potential will be high for
another active wildfire season this spring once again. Longer term outlooks
suggest summer rainfall could be influenced by another active hurricane
season.
•
The next forecast will be the first week in April, 2008. Should there be any
questions, please contact Deborah Hanley at [email protected].
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National Weather Service
• National Weather Service
– Products produced for:
• Fire Weather Zones
– Products produced by:
• Meteorologists
– Products geared toward:
• Tactical planning
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NWS: Fire Weather Planning Forecast
FNUS52 KJAX 171939FWFJAXFIRE WEATHER PLANNING FORECAST FOR NORTHEAST
FLORIDA/SOUTHEAST GEORGIANATIONAL WEATHER SERVICE JACKSONVILLE FL239 PM
EST THU JAN 17 2008DISCUSSION...
• A narrative or
tabular zone-type
product
• Here, will most
likely be for JAX
• Elements
include:
– Sky/weather
– Temperature
– Relative humidity
LOW PRESSURE WILL TRACK ACROSS THE FORECAST AREATHIS EVENING AND PUSH
NORTHEAST OF THE REGION TONIGHT. SCATTEREDSHOWERS WILL DISSIPATE
THROUGH THE EVENING HOURS. WEAK HIGH PRESSUREWILL BUILD INTO THE REGION
ON FRIDAY. ANOTHER LOW WILL DEVELOP INTHE GULF OF MEXICO SATURDAY AND
TRACK NORTHEAST OF THE REGIONSETTING THE STAGE FOR A COLD...BRISK AND DRY
SUNDAY WITH HIGHPRESSURE SETTING UP OVER THE REGION EARLY NEXT WEEK.
RELATIVE HUMIDITIES WILL REMAIN ABOVE CRITICAL LEVELS THROUGH THE
PERIODEXCEPT FOR SUNDAY WHEN RH VALUES WILL BOTTOM OUT IN THE 15-25
PERCENTRANGE OVER THE INLAND SECTIONS AND RED FLAG WARNINGS MAY BE
REQUIRED.WINDS LESS THAN 15 MPH ARE EXPECTED ON FRIDAY. NORTHWEST WINDS
OF15 TO 20 MPH ARE EXPECTED ON SATURDAY. NORTH WINDS OF 15 TO 20 MPHARE
EXPECTED ON SUNDAY. NORTHEAST WINDS OF 15 TO 20 MPH WILLCONTINUE ON
MONDAY AND SLOWLY DECREASE TO LESS THAN 15 MPH ONTUESDAY AND
WEDNESDAY.GAZ153-154-165-166-181045-INLAND GLYNN-COASTAL GLYNN-INLAND
CAMDEN-COASTAL CAMDEN-239 PM EST THU JAN 17 2008
TONIGHT
FRI
FRI NIGHT SATCLOUD COVER
PCLDY
PCLDY
MCLDY
MCLDYCHANCE
PRECIP (%) 0
0
80
80WEATHER TYPE
NONE
SHOWERS
SHOWERS
SHOWERSTEMP
43
59
45
55RH (%)
97
60
100
7020FT WND MPH (AM)
N 6
N 8 G2120FT WND
MPH (PM) NW 8
N 4
NE 4
NW 14 G26PRECIP DURATION
11
11PRECIP BEGIN
7 PM
CONTINUINGPRECIP END
7 AM
CONTINUINGPRECIP AMOUNT
0.00
0.00
0.69
0.87LAL
1
1
1
1MIXING HEIGHT(FT-AGL) 500
2200
400
1600TRANSPORT WND (MPH) N 13
N 7
NE 7
NW 30DISPERSION INDEX
7
15
5
27MAX LVORI
6
9REMARKS...NONE..FORECAST FOR
DAYS 3 THROUGH 7....SUNDAY...PARTLY CLOUDY. A 20 PERCENT CHANCE OF RAIN
SHOWERS.LOWS IN THE UPPER 20S. HIGHS IN THE LOWER 50S. NORTHEAST WINDS15
TO 20 MPH..MONDAY...PARTLY CLOUDY. LOWS IN THE LOWER 30S. HIGHS IN THEUPPER
50S. NORTHEAST WINDS 10 TO 15 MPH..TUESDAY...MOSTLY CLOUDY. A 50 PERCENT
CHANCE OF RAIN SHOWERS.LOWS IN THE MID 40S. HIGHS IN THE LOWER 60S. EAST
WINDS 5 TO10 MPH..WEDNESDAY THROUGH THURSDAY...MOSTLY CLOUDY WITH A 50
PERCENTCHANCE OF RAIN SHOWERS. LOWS IN THE LOWER 50S. HIGHS IN THE UPPER
60S. SOUTHWEST WINDS 5 TO 15 MPH.
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NWS: Fire Weather
Watches / Red Flag
Warnings
• Issued when the combination of
dry fuels and weather conditions
support extreme fire behavior or
ignition is occurring or expected
to occur.
• Can prevent prescribed burning
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Fire Weather Watches
• Issued when there is a high potential for the
development of a Red Flag Event.
• Normally issued 24 to 72 hours in advance.
FIRE WEATHER WATCH NATIONAL WEATHER SERVICE
MIDLAND/ODESSA TX 946 AM CST FRI JAN 27 2006
...FIRE WEATHER WATCH IN EFFECT SATURDAY FOR THE
GUADALUPE MOUNTAINS FOR RELATIVE HUMIDITIES OF 15
PERCENT OR LESS...SUSTAINED 20 FOOT WINDS OF 20 MPH
OR GREATER AND HIGH FIRE DANGER...
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Red Flag Warnings
• Used to warn of an impending, or occurring Red
Flag event.
Red Flag Warning/Fire Weather Watch Information
...RED FLAG WARNING IN EFFECT ACROSS THE SUWANNEE VALLEY
REGION OF NORTH FLORIDA FROM NOON TO 5 PM EST THIS AFTERNOON
FOR LONG DURATIONS OF LOW RELATIVE HUMIDITY...
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Spot Weather Forecast– DOF in Florida–
must have local information and location
Florida Division of Forestry - Spot Forecast
Forecast ID: 1185873416
Date Issued: Tue Jul 31, 2007 at 05:16
Name: Leda Kobziar
Company: University of Florida
Location: 29.74 / -82.21
• Site specific
forecasts
that are
issued to fit
time,
topography
and weather
of a specific
location.
Forecast
Time
Temp
Humidity
Wind
Speed
Direction
Cloud
Cover
5:00
76-79
85-90%
3-6
WNW
BK
6:00
77-80
84-89%
3-6
WNW
BK
7:00
77-80
83-88%
4-7
WNW
BK
8:00
78-81
83-88%
4-7
WNW
BK
9:00
80-83
78-83%
4-7
WNW
BK
10:00
82-85
74-79%
4-7
WNW
BK
11:00
83-86
70-75%
4-7
NW
SC
12:00
84-87
68-73%
4-7
SSW
SC
Precip
13:00
85-88
66-71%
5-8
ESE
SC
12%
Chance
(Trace)
14:00
86-89
64-69%
5-8
N
BK
15%
Chance
(Trace)
BK
12%
Chance
(Trace)
15:00
85-88
65-70%
5-8
NNE
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Complete Exercise 5
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