State of Atmosphere surrounding the earth, conditions at specific time.
Weather at given place or area over time
weather conditions that influence: fire starts, fire behavior, fire control
periods of year when fire is likely to occur and cause damage.
Types of fire season
Single period, Two period, and Year long
14.7 lb/sq in.
degree of hotness or coldness
boundary between two air masses of different temps and moisture
contribution of water to atmospheric pressure
Saturation vapor pressure
Vapor pressure when air contains all the water it can hold. depends on temp.
What happens to Saturation vapor pressure as temperature increases?
As temp increases, more water can be held and saturation vapor pressure increases
actual amount of water vapor in a set volume of air, lbs/ft^3
Absolute humidity/Saturation humidity X 100= %. how much water is actually there compared to how much it can hold.
Basic Rule of RH
RH doubles with each 20 F drop in temp.
the temp when water vapor turns to water
How does the Lapse rate work?
lapse rate less than adiabatic (5.5ft) is considered stable because there isn't that much vertical motion. Higher and it's unstable because fire can easily move air vertically and feed itself.
resistance of the atmosphere to vertical motion.
change in temp/1000 ft. elevation.
dry adiabatic lapse rate
5.5 F change per 1000 ft
Explain Low Pressure system in the N. Hemisphere
Airflow is counter-clockwise and spirals inward, moves air up because the surface of the earth doesn't let it move down.
Airflow into a low pressure system from all sides
Explain high pressure system in the N. Hemisphere
Airflow is clockwise and spiral outward, moves air down because it pulls air from aloft.
Airflow away from a high pressure system.
Lifting processes of Air
thermal, orographic or frontal
column of air that rises because of pocket of hot air, cold air replaces the hot air on the surface. Causes dust devils.
air forced up the windward sides of slopes. Air cools at mountain tops and precipitation occurs.
Air is forced up the slope of either a warm or cold front by regional winds.
winds that blow over mountain ranges and descend the slope. If the down-flowing wind is warm and dry, it's a Foehn wind. Wind moving from high pressure to low pressure.
Sea and land breeze
Inland sea breeze from noon till sunset.
upslope wind develops as mountain surfaces heat up. Downslope wind develops in late afternoon because mountain surface cools faster.
Cumulus/cumulonumbus clouds are most important to fire behavior. Form near tip of rising convection columns, cause erratic weather.
violent local storm produced by cumulonimbus cloud. crazy weather
Old system of Wildland fire terminology
wildfire, prescribed natural fire, prescribed fire
prescribed natural fire
managed lightning ignition
human ignited manged fire
New system of Wildland fire terminology
Wildlands fires:a)wildfires, b)prescribed fires
general term describing any non structure fire that occurs in a wildland.
unplanned ignitions or prescribed fires that are declared wildfires
what is the initial action on human caused wildfire?
suppression at the lowest cost with fewest negative consequences to firefighter and public safety.
what is the management response to wildand fire on federal land?
based on the objective established in the resource or fire management plan.