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LOW
≤50
MODERATE
50-75
HIGH
75-90
VERY HIGH
90-97.5
EXTREME
≤97.5


The Chandler Burning Index (CBI) uses the air temperature and relative humidity to calculate a numerical index of fire danger. That number is then equated to the Fire Danger severity of either extreme, very high, high, moderate, or low. It's based solely on weather conditions, with no adjustment for fuel moisture. Here on the K3JAE Weather site, the CBI is calculated from the current weather conditions and reflects the current calculated fire danger. The National Weather Service calculates a 30 day Chandler Burning Index based on forecasted weather conditions for the month.

The monthly fire potential is represented by a modified version of the Chandler Burning Index (CBI). CBI provides a measure of the effects of average monthly temperature and humidity on fire intensity and rate of spread (not the same as NFDRS rate of spread). Both the intensity and spread components of the Index are linearly related to temperature (an increase in temperature results in a proportionately higher Index), but are exponentially related to humidity (a small decrease in humidity results in a large increase in the Index). The modified version of the Chandler Burning Index is computed from:

CBI = (((110 - 1.373*RH) - 0.54 * (10.20 - T)) * (124 * 10**(-0.0142*RH)))/60

where:

RH = forecast monthly mean afternoon relative humidity (percent)
T = forecast monthly mean afternoon temperature (degrees Celsius)

The Chandler Burning Index has been shown to be highly correlated with monthly fire activity.