Monthly Fire Weather Forecast:
Description of Monthly Fire Weather Forecast
The monthly fire weather forecasts can provide fire managers with a
quick and easy planning tool. This forecast package was prepared by
the Fire Meteorology Research Work Unit, USDA Forecast Service, Forest
Fire Laboratory, Riverside, California. It is based on the monthly
forecast of 700 millibar heights issued by the NWS Climate Analysis
Center in Washington, DC. The forecasts are not the fire planner's
magic bullets, but they do provide scientifically based, long-range
forecasts. Because these forecasts are inherently less accurate in the
long range than in the short range, the user must consider the impact
of variable forecast accuracy. Where average weather conditions may
vary rapidly over short distances, as in complex terrain, the scale of
these forecasts may be too coarse to capture such variations
accurately. For more details on the monthly forecasts, see
McCutchan et al., 1991.
Description of Monthly Fire Potential and the Chandler Burning Index
The monthly fire weather forecast characterizes the weather-induced
fire potential for the continental United States as an average for the
month. The color maps depict percentiles that are similar to those
derived in the National Fire-Danger Rating System. Higher percentiles
indicate higher than normal fire potential. 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: see Chandler et
al. 1983). 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 (McCutchan and Main,
1989).
References:
Chandler, C.; Cheney, P.; Thomas P.;Trabaud L. and Williams, D. 1983.
Fire in Forestry, Vol. I: Forest Fire Behavior and Effects.
John Wiley & Sons, New York, NY. 450 pp.
McCutchan, Morris H.; Meisner, Bernard N.; Fujioka, Francis M.;
Benoit, John W. and Ly, Benjamin B. 1991. Monthly Fire Weather
Forecasts. Fire Management Notes. 52(3):41-47
McCutchan, Morris H. and Main, W. A. 1989. The Relationship
Between Mean Monthly Fire Potential Indices and Monthly Fire Severity.
In Proceedings, 10th Conference on Fire and Forest Meteorology;
1989 April 17-21; Ottawa, Ontario, Canada. Forestry Canada. 430-435.
Lin, K. M. Y. and Fujioka, Francis M. 1995. Error Analysis of
Monthly Fire Weather Forecasts. In Proceedings, Sixth
International Meeting on Statistical Climatology, 19-23 June 1995,
Galway, Ireland. 6p.
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Direct comments or questions about the Monthly Fire Weather Forecast to
ffujioka@fs.fed.us
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