Firefighter's Handbook On Wildland
Firefighting 4th edition
Weather factors that can affect the start & spread of wildland fires are: - -
Wind
Relative Humidity
Temperature
Precipitation
- Cause of most wildland fire injuries & death - -Change in weather
- Troposphere - -Layer of atmosphere closest to the ground (5-10 miles
thick). All weather phenomena (thunderstorms,wind, humidity) occur here.
- From a wildland perspective, 2 most important components of the
atmosphere are: - -Oxygen & Water Vapor
- When does most solar radiation reach the Earth's Northern hemisphere? -
-June
- Ultimate source of all weather is: - -The Sun (Solar Radiation)
- Heat Balence - -To maintain a favorable climate, the daily outgoing
radiation must equal the incoming solar radiation. The imbalance leads to
WEATHER FRONTS.
- 4 primary factors that influence Weather Fronts are: - --Amount of
moisture and/or pollution in the air.
-The angle between the surface of the earth & the sun.
-Lag time when solar radiation strikes the Earth & when the heat is radiated
back into space.
-The surface properties of the terrain and/or vegetation.
- Water absorbs and holds (more/less) heat energy than rock. - -Water
absorbs and holds MORE heat energy than rock.
- -Has the greatest impact on fire behavior of any of the weather factors. - -
Wind
- Wind is defined as: - -Horizontal movement of air.
- General winds - -Affect large areas. These are the winds that are reported
in the daily weather forecasts.
,- Local Winds - -Produced by features of the local terrain.
- Surface Winds - -Normally measured at 20 feet above the ground.
- Mid-Flame Winds - -Occur at the midpoint of the flame height, have the
GREATEST effect on the direction a fire will burn.
- Uneven heating on the Earth's surface creates atmospheric pressure
differences called: - -Pressure Gradients
- Don't ever forget to factor the - - into your plans. - -Predicted Winds
- Coriolis Effect/Force - -Force of the Earth's rotation on the moving air
causes the air (wind) to rotate in a counter-clockwise direction north of the
equator, and clockwise south of the equator.
- Isobars - -Points of equal atmospheric pressure are shown with a line,
similar to a contour line.
- Wind speed is determined by the - -Pressure Gradient
- Wind direction is determined by the relationship of the - -Highs to the
lows.
- Air moves around a HIGH-pressure cell in a - -Clockwise direction
- Air moves around a LOW-pressure cell in a - -Counterclockwise direction.
- If you have your back to the general wind: - -Low-pressure is to your left &
high pressure is to your right
- Cold air is displacing warm air: - -Cold Front
- Warm air is displacing cooler air: - -Warm Front
- Warm air mass rides up and over a colder air mass: - -Occluded Front
- Area of low-pressure is called a - -Trough
- Ridges - -High-pressure, with descending air & a minimum of cloudiness
and precipitation.
- "Weather Centers" During the summer, the weather map is dominated by
the: - -Pacific, Bermuda Highs & California Low.
, - "Weather Centers" During the winter, the map shows the: - -Great Basin
and the Arctic Highs
- Sea Breeze - -Light winds that blow from the water onto the land. Cool
with higher RH. Fog or low clouds may be associated. Can lower the level of
fire behavior.
- Land Breeze - -Occurs at night when land is cooler than nearby water.
Moves from the land out over the sea.
- Slope Winds - -Daily, local winds that flow upslope during the day, then
downslope at night. Upslope are more stronger than downslope.
- Valley winds - -Sun warms higher elevations first, drawing cooler air from
below. Starts Late morning, when air in valley is warmed. "Don't
underestimate the impact that valley winds can have on fire behavior."
- 4 Problem Winds for Firefighters - -Cold front winds
Foehn or gravity winds
Winds associated with thunderstorms
Whirlwinds (Dust Devils or Firewhirls)
- Cold Front Winds - -Winds shift direction, may adversely affect fire
behavior.
Ahead of an approaching cold front, winds shift gradually from southeast to
south & onto Southwest. As the cold front passes, winds shift rapidly to west
then northwest.
- Foehn Winds or Gravity Winds - -Warm, dry wind that occurs when air
spills over high elevations & moves downhill high speed. Compresses,
becoming warmer & drier.
Santa Ana, Chinook, North, & Eastern Winds.
- Thunderstorm Downdrafts; Thunderstorms (Cumulonimbus Clouds) - -
Develop when there is adequate atmospheric moisture, instability, & forces
that will cause air to rise. Downdrafts through the center of clouds,
dangerous in all directions. Lasts less than 12hrs. Starts in the afternoon,
concludes before midnight. Look for:
-base of cloud begins to 'Roll' on the downward side.
-Virgo begins to hang underneath.
-dust clouds seen on ground.
- Whirlwinds, Dust Devils, & Firewhirls - -Miniature cyclones that are caused
when strong convection currents & updrafts develop. Look for:
-Mostly clear skies or clouds
-light surface winds
Firefighting 4th edition
Weather factors that can affect the start & spread of wildland fires are: - -
Wind
Relative Humidity
Temperature
Precipitation
- Cause of most wildland fire injuries & death - -Change in weather
- Troposphere - -Layer of atmosphere closest to the ground (5-10 miles
thick). All weather phenomena (thunderstorms,wind, humidity) occur here.
- From a wildland perspective, 2 most important components of the
atmosphere are: - -Oxygen & Water Vapor
- When does most solar radiation reach the Earth's Northern hemisphere? -
-June
- Ultimate source of all weather is: - -The Sun (Solar Radiation)
- Heat Balence - -To maintain a favorable climate, the daily outgoing
radiation must equal the incoming solar radiation. The imbalance leads to
WEATHER FRONTS.
- 4 primary factors that influence Weather Fronts are: - --Amount of
moisture and/or pollution in the air.
-The angle between the surface of the earth & the sun.
-Lag time when solar radiation strikes the Earth & when the heat is radiated
back into space.
-The surface properties of the terrain and/or vegetation.
- Water absorbs and holds (more/less) heat energy than rock. - -Water
absorbs and holds MORE heat energy than rock.
- -Has the greatest impact on fire behavior of any of the weather factors. - -
Wind
- Wind is defined as: - -Horizontal movement of air.
- General winds - -Affect large areas. These are the winds that are reported
in the daily weather forecasts.
,- Local Winds - -Produced by features of the local terrain.
- Surface Winds - -Normally measured at 20 feet above the ground.
- Mid-Flame Winds - -Occur at the midpoint of the flame height, have the
GREATEST effect on the direction a fire will burn.
- Uneven heating on the Earth's surface creates atmospheric pressure
differences called: - -Pressure Gradients
- Don't ever forget to factor the - - into your plans. - -Predicted Winds
- Coriolis Effect/Force - -Force of the Earth's rotation on the moving air
causes the air (wind) to rotate in a counter-clockwise direction north of the
equator, and clockwise south of the equator.
- Isobars - -Points of equal atmospheric pressure are shown with a line,
similar to a contour line.
- Wind speed is determined by the - -Pressure Gradient
- Wind direction is determined by the relationship of the - -Highs to the
lows.
- Air moves around a HIGH-pressure cell in a - -Clockwise direction
- Air moves around a LOW-pressure cell in a - -Counterclockwise direction.
- If you have your back to the general wind: - -Low-pressure is to your left &
high pressure is to your right
- Cold air is displacing warm air: - -Cold Front
- Warm air is displacing cooler air: - -Warm Front
- Warm air mass rides up and over a colder air mass: - -Occluded Front
- Area of low-pressure is called a - -Trough
- Ridges - -High-pressure, with descending air & a minimum of cloudiness
and precipitation.
- "Weather Centers" During the summer, the weather map is dominated by
the: - -Pacific, Bermuda Highs & California Low.
, - "Weather Centers" During the winter, the map shows the: - -Great Basin
and the Arctic Highs
- Sea Breeze - -Light winds that blow from the water onto the land. Cool
with higher RH. Fog or low clouds may be associated. Can lower the level of
fire behavior.
- Land Breeze - -Occurs at night when land is cooler than nearby water.
Moves from the land out over the sea.
- Slope Winds - -Daily, local winds that flow upslope during the day, then
downslope at night. Upslope are more stronger than downslope.
- Valley winds - -Sun warms higher elevations first, drawing cooler air from
below. Starts Late morning, when air in valley is warmed. "Don't
underestimate the impact that valley winds can have on fire behavior."
- 4 Problem Winds for Firefighters - -Cold front winds
Foehn or gravity winds
Winds associated with thunderstorms
Whirlwinds (Dust Devils or Firewhirls)
- Cold Front Winds - -Winds shift direction, may adversely affect fire
behavior.
Ahead of an approaching cold front, winds shift gradually from southeast to
south & onto Southwest. As the cold front passes, winds shift rapidly to west
then northwest.
- Foehn Winds or Gravity Winds - -Warm, dry wind that occurs when air
spills over high elevations & moves downhill high speed. Compresses,
becoming warmer & drier.
Santa Ana, Chinook, North, & Eastern Winds.
- Thunderstorm Downdrafts; Thunderstorms (Cumulonimbus Clouds) - -
Develop when there is adequate atmospheric moisture, instability, & forces
that will cause air to rise. Downdrafts through the center of clouds,
dangerous in all directions. Lasts less than 12hrs. Starts in the afternoon,
concludes before midnight. Look for:
-base of cloud begins to 'Roll' on the downward side.
-Virgo begins to hang underneath.
-dust clouds seen on ground.
- Whirlwinds, Dust Devils, & Firewhirls - -Miniature cyclones that are caused
when strong convection currents & updrafts develop. Look for:
-Mostly clear skies or clouds
-light surface winds
