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WEATHER . Fire Weather. *Click on image to play video. CPBM Objectives. Describe the various types of wind and how wind influences fire behavior. Understand the temp/humidity relationship. Define stability, inversion, mixing height, dispersion index and transport wind speed.

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fire weather
Fire Weather

*Click on image to play video

cpbm objectives
CPBM Objectives
  • Describe the various types of wind and how wind influences fire behavior.
  • Understand the temp/humidity relationship.
  • Define stability, inversion, mixing height, dispersion index and transport wind speed.
  • List the methods by which heat is transferred, and how weather affects these.
  • Explain the sea breeze process and the possible effects on Rx fires.
cpbm objectives4
CPBM Objectives
  • Describe the passage of a typical cold front in Florida, particularly as it relates to wind and temperature.
  • List the influences of thunderstorms on fire behavior.
  • Understand the differences and usages of the daily planning, spot, red flag event and other weather forecasts.
  • Use a Belt Weather Kit to take a representative weather observation.
  • Discuss the steps in obtaining a spot weather forecast.
temperature
Temperature
  • The hotness/coldness of a substance
  • Reflects average molecular activity (thermal energy)
    • Fahrenheit
    • Celsius
    • Kelvin (0 = no molecular activity)
slide6

What influences air temperature?

    • Time of day
    • Season
    • Elevation
    • Topography
    • Latitude
    • Weather systems
    • Bodies of water

Why does air temperature matter in wildland fires?

heat vs temperature
Heat vs. Temperature
  • Heat Energy
    • Can be converted to other energy forms
    • Can be transferred from one substance to another
  • Temperature
    • Determines direction of net heat transfer (hot to cold)
temperature change depends on molecular structure heat capacity
Temperature change depends on molecular structure (“Heat Capacity”)

Examples of Specific Heats (relative to water)

  • Water: 1.0
  • Forests: 0.45 - 0.65
  • Dry Air: 0.24
  • Dry Soil/Rock: 0.20
  • Gasoline: 0.50
slide11

SUMMER

WINTER

atmospheric reaction
Atmospheric Reaction
  • Unequal heating of the earth.
  • Energy absorbed and energy released are not in balance at any one time and place.
winds
Winds

Horizontal movement of air

*Click on image to play video

winds wind s effect on wildland fire
WindsWind’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.
general winds
General Winds

*Click on image to play video

local winds
Local Winds

*Click on image to play video

local winds slope winds
Local WindsSlope 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
local winds valley winds
Local WindsValley 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.
sea breeze 1998 perry fire
Sea Breeze1998 Perry Fire

Sea breeze interacting with Perry fire. Fire activity increases when sea breeze front penetrates fire.

seasonal weather
Seasonal Weather

*Click on image to play video

winter weather in fl cold fronts
Winter Weather in FLCold Fronts

*Click on image to play video

cold front passage
Cold Front Passage
  • Wind shifts as the front passes
    • clockwise SW to W/NW
  • Winds increase in speed
  • Air becomes drier

Implications for fire?

-Rx fire

-wildfire

relative humidity
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%
slide29

Temperature and RH Relationships

3 grams

3 grams

3 grams of H2O

50ºF

70ºF

90ºF

100%

(saturated)

50%

(unsaturated)

25%

(unsaturated)

thermograph
Thermograph

Temperature and RH Relationship

rh and fire
RH and Fire
  • Fuel Moisture

-fine versus large fuels?

  • Why does this matter
    • wildland fire suppression
    • Rx burning

Small changes in RH that aren’t noticed can have significant impacts

  • Monitoring (belt weather kit) is crucial!!
precipitation
Precipitation

Liquid or solid water particles that originate in the atmosphere, and become large enough to fall to the earth’s surface.

precipitation amount vs duration
PrecipitationAmount vs. Duration
  • Fine Fuels
    • gain and losemoisture 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

Keetch/Byram Drought Index (KBDI: 0 to 800)

atmospheric stability
Atmospheric Stability

The degree to which vertical motion in the atmosphere is ENHANCED or SUPPRESSED.

*Click on image to play video

atmospheric stability35
AtmosphericStability
  • Depends on the vertical temperature distribution of the atmosphere
  • Unstable air encourages vertical motion
atmospheric stability36
AtmosphericStability
  • Environmental Lapse Rate
    • Change in temperature with height within the air column
    • Varies widely depending on conditions (average 3.5˚F/1000ft)
    • Determines atmospheric stability
  • Adiabatic Lapse Rate
    • Change in temperature solely due to change in air pressure (when a parcel of air is physically moved)
    • Dry (unsaturated): 5.5˚F/1000ft
    • Moist (saturated): 2.5˚F/1000ft is typical
stable atmosphere
Stable Atmosphere

Stable atmosphere resists upward vertical motion

*Click on image to play video

stable atmosphere visual indicators
Stable AtmosphereVisual Indicators
  • Visual Indicators
    • Clouds form in layers
    • Smoke drifts apart after limited rise
    • Poor visibility due to smoke or haze
    • Fog layers
    • Steady winds
stable atmosphere visual indicator examples
Stable AtmosphereVisual Indicator Examples
  • Smoke drifts apart after limited rise
stable atmosphere inversion types
Stable AtmosphereInversion Types
  • Four Inversion Types
    • Nighttime (Radiation)
    • Frontal
    • Marine
    • Subsidence
  • Two most common types
    • Nighttime (Radiation)
    • Subsidence
stable atmosphere thermal belt
Stable AtmosphereThermal 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
unstable atmosphere
Unstable Atmosphere

Encouraging upward vertical motion

unstable atmosphere visual indicators
Unstable AtmosphereVisual Indicators
  • Visual Indicators
    • Clouds grow vertically and smoke rises to great heights
    • Cumulus clouds
    • Good visibility
    • Gusty winds
    • Dust devils and firewhirls
unstable atmosphere visual indicator examples
Unstable AtmosphereVisual Indicator Examples
  • Clouds grow vertically and smoke rises to great heights
unstable atmosphere visual indicator examples49
Unstable AtmosphereVisual Indicator Examples
  • Gusty Winds
  • Dust devils and firewhirls

*Click on image to play video

atmospheric stability50
Atmospheric Stability
  • Mixing Height (500m minimum!)
  • Atmospheric Dispersion Index (ADI)

0

40

70

Poor to Fair

May be too stagnant for Rx Burning (smoke issues)

Good

Preferred range for Rx Burning

Very Good

May be too hazardous for Rx Burning (control issues)

  • LVORI (low visibility occurrence risk)
    • Calculated from ADI and relative humidity
    • Associated with risk of vehicle accidents
    • Range 0-10
critical fire weather
Critical Fire Weather

*Click on image to play video

critical fire weather cold fronts
Critical Fire WeatherCold Fronts

*Click on image to play video

critical fire weather foehn winds
Critical Fire WeatherFoehn Winds

*Click on image to play video

critical fire weather foehn winds54
Critical Fire WeatherFoehn Winds
  • Common Foehn Winds
    • Chinook
    • Wasatch
    • North
    • East
    • Santa Ana
slide57

Move with the general winds

  • Downdrafts
  • Erratic/gusty winds
  • Very common in FL
  • Virga (western US)
planning and implementation
Planning and Implementation
  • Forecasts
    • ‘regular’ weather forecasts
    • fire weather forecasts
    • Planning (long and short term)
  • On-Site Wx Observations
    • Rx burning
    • wildand fire use
    • fire suppression
predictive services national regional websites
Predictive Services (national, regional websites)
  • Season Fire Potential
  • Extended Outlooks
    • 3-14 days
    • month, 3 months
  • Daily
  • Spot Weather Forecast
    • Specific to burn site
    • On request
slide61

Spot Weather Forecast– DOF in Florida– must have local information and location

  • Site specific forecasts that are issued to fit time, topography and weather of a specific location.
slide62

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
slide63

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...

slide64

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...

slide65
National Weather Service
  • http://www.srh.noaa.gov/jax/
  • Florida Division of Forestry
  • http://www.fl-dof.com/wildfire/index.html