Fire Danger Rating and Weather

Fire danger is the probability of a fire to start, the rate of spread and intensity of its burn. This Animation: Antique weather station.probability is influenced by fuel type, fuel moisture, amount of fuel, and slope of the land area. Another important influence is weather, particularly wind and relative humidity.

When relative humidity is below 50%, prescribed burning during the summer does best. During the Spring or Fall Fire Season, a relative humidity below 40% can mean that any wildfires will be difficult to control. Wind causes a fire to burn more intensely, and increases the spread of fire by carrying hot embers to new fuel sources. Fuels with a low Fuel Moisture will burn very hot.

Weather data (temperature, relative humidity, wind direction, wind speed, and rainfall in the last 24 hours) from National Weather Service stations and local forestry offices is analyzed every morning. This analysis results in a predicted fire danger class day, which is broadcast statewide at 10 am daily. When conditions are critical by 2 pm, the day's weather data has been analyzed and an actual fire danger class day is broadcast statewide if necessary.

Fire Occurrence Levels and Response Actions - General Fire Danger Map

  • Level 1 - Class Day 1
    LOW
    Fires do not readily start.
    Fires that do start spread slowly with low resistance to control.
    ACTION: Use local resources per Memorandum of Understanding (MOU), cooperative agreement. When required resources exceed those available from local DOF, resources from cooperating agencies will be activated locally as needed.
  • Level 2 - Class Day 2
    MODERATE
    Fires can start from most accidental causes, but the number of starts is generally low.
    Fires burn at moderate intensities, heavy fuel concentrations will burn hot.
    ACTION: Use local resources per cooperative agreement. When required resources exceed those available from local DOF, resources from cooperating agencies as needed.
  • Level 3 - Class Day 3
    HIGH
    Fires start easily from most causes.
    Control of fires can become difficult if initial attack not initiated promptly, especially in heavy fuels.
    Most fires controlled within first burning period.
    ACTION: Use local resources per cooperative agreement. When required resources exceed those available from local DOF, resources from cooperating agencies will be activated as needed. Resources will be on standby in accordance with need and Agency MOU.
  • Level 4 - Class Day 4
    VERY HIGH
    Fires start readily and spread quickly.
    Resistance to control is high, as is the potential for large fires.
    Fire behavior is often erratic,“blow up”potential is high.
    ACTION: When required resources exceed those available from local DOF, resources from cooperating agencies will be activated as needed and selected agency resources will be places on standby in area.
  • Level 5 - Class Day 5
    EXTREME
    Severe fire conditions, potential for fire disaster is high.
    Direct attack of fires is virtually impossible, fires often escape initial attack.
    Fire behavior is erratic, “blow ups” may be expected.
    Resistance to control is high, fires not usually controlled until burning subsides.
    ACTION: When required resources exceed those available from local and regional DOF, resources from cooperating agencies will be activated as needed and selected agency resources will be placed on standby statewide.

A Declared Forest Fire Emergency may occur at any level when a major commitment of resources from other agencies or the National Guard are needed.

Virginia Eastern Standard time = Zulu time - 5 hours. Virginia Daylight Savings Time = Zulu time - 4 hours.

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Last modified: Wednesday, 24-Sep-2014 13:00:18 EDT