Fire Weather Index

Fire Weather Data for the San Diego - Mission Trails Weather Station.

Last Updated: 9/9/2024 12:05:51 PM

Last Parse Time: 12:02

The diagram below illustrates the components of the FWI System. Calculation of the components is based on consecutive daily observations of temperature, relative humidity, wind speed, and 24-hour rainfall. The six standard components provide numeric ratings of relative potential for wildland fire.

Severity Table

Fine Fuel Moisture Code

The Fine Fuel Moisture Code (FFMC) is a numeric rating of the moisture content of litter and other cured fine fuels. This code is an indicator of the relative ease of ignition and the flammability of fine fuel.

Duff Moisture Code

The Duff Moisture Code (DMC) is a numeric rating of the average moisture content of loosely compacted organic layers of moderate depth. This code gives an indication of fuel consumption in moderate duff layers and medium-size woody material.

Drought Code

The Drought Code (DC) is a numeric rating of the average moisture content of deep, compact organic layers. This code is a useful indicator of seasonal drought effects on forest fuels and the amount of smoldering in deep duff layers and large logs.

Initial Spread Index

The Initial Spread Index (ISI) is a numeric rating of the expected rate of fire spread. It combines the effects of wind and the FFMC on rate of spread without the influence of variable quantities of fuel.

Buildup Index

The Buildup Index (BUI) is a numeric rating of the total amount of fuel available for combustion. It combines the DMC and the DC.

Fire Weather Index

The Fire Weather Index (FWI) is a numeric rating of fire intensity. It combines the Initial Spread Index and the Buildup Index.
The FWI predicts the risk of wild fire for the mid afternoon (peak fire danger time usually 2:00 to 4:00 pm).

FIRE DANGER CODES (FFDC, SFDC, GFDC)

The FWI is further refined into indices that represent the Fire Intensity likely in the three vegetation types (Forest, Scrub & Grasses). These three codes are divided into five fire danger classes (Low, Moderate, High, Very high & Extreme) and calculate the fire intensity in kilowatts per square metre (kw/m^2).

LOW (0..10kw/m^2), MODERATE (11-500kw/m^2), HIGH (501-2000kw/m^2), VERY HIGH (2001-4000kw/m^2), EXTREME (4000+kw/m^2)

FFDC (Forest Fire Danger Code)

Based on predicted generated "fire intensity (kw/m^2)" in highly flammable forest type vegetation (conifer, eucalypt). This code denotes how difficult it would be to control a fire in this vegetation type should one start.

SFDC (Scrub Fire Danger Code)

Based on predicted generated "fire intensity (kw/m^2)" in flammable scrub type vegetation (tea tree, broom, gorse, manuka). This code denotes how difficult it would be to control a fire in this vegetation type should one start.

GFDC (Grass Fire Danger Code)

Based on predicted generated "fire intensity (kw/m^2)" in grass type vegetation (dry grass, tussock). This code denotes how difficult it would be to control a fire in this vegetation type should one start.