# ESPM 181A pg16-18

## 41 terms · Fire Weather pg 16-18

### Weather

State of Atmosphere surrounding the earth, conditions at specific time.

### Climate

Weather at given place or area over time

### Fire Weather

weather conditions that influence: fire starts, fire behavior, fire control

### Fire Season

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.

### Air temperature

degree of hotness or coldness

### Front

boundary between two air masses of different temps and moisture

### Vapor pressure

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

### Absolute humidity

actual amount of water vapor in a set volume of air, lbs/ft^3

### Relative humidity

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.

### Dew point

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.

### Atmospheric stability

resistance of the atmosphere to vertical motion.

### Lapse rate

change in temp/1000 ft. elevation.

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.

### Convergence

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.

### Divergence

Airflow away from a high pressure system.

### Lifting processes of Air

thermal, orographic or frontal

### Thermal lifting

column of air that rises because of pocket of hot air, cold air replaces the hot air on the surface. Causes dust devils.

### Orographic lifting

air forced up the windward sides of slopes. Air cools at mountain tops and precipitation occurs.

### frontal lifiting

Air is forced up the slope of either a warm or cold front by regional winds.

### Foehn 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.

### Slope wind

upslope wind develops as mountain surfaces heat up. Downslope wind develops in late afternoon because mountain surface cools faster.

### clouds

Cumulus/cumulonumbus clouds are most important to fire behavior. Form near tip of rising convection columns, cause erratic weather.

### Thunderstorm

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

### prescribed fire

human ignited manged fire

### New system of Wildland fire terminology

Wildlands fires:a)wildfires, b)prescribed fires

### Wildand Fire

general term describing any non structure fire that occurs in a wildland.

### Wildfires

unplanned ignitions or prescribed fires that are declared wildfires

planned ignition

### 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.

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