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WFAS is currently based on weather observations taken
at fire weather stations throughout the U.S. and entered into the
Weather Information Management System (WIMS). NFDRS calculations
are done at the National Computer Center at Kansas City (NCC-KC).
The fuel model, index, and fire danger levels are set by local
managers. National WFAS maps are produced from fire danger levels
using simple inverse distance square interpolation. Satellite
"greenness" products are currently stand-alone indicators of fire
potential and not integrated into the calculations except in the
experimental projects.
NFDRS-based products:
- NFDRS fire weather
- NFDRS dead fuel moisture
- Fire danger, adjective rating
Satellite NDVI-derived products:
- Visual Greenness
- Relative Greenness
- Departure from average
The NFDRS-based products in WFAS are generated as follows:
- Fire weather observations are recorded once per day in
mid-afternoon (2 p.m. LST) at each of about 1500 weather stations
in the Fire Weather Network. Many of the stations are, however,
seasonal and report weather only during the fire season, which
varies by location.
- Weather observations are reported to the Weather Information
Management System (WIMS). National Fire Danger Rating System
(NFDRS) calculations are done at the National Computer Center in
Kansas City. Weather observations and site descriptors are used to
calculate fuel moistures and fire danger indexes. Local managers
select the index and cutoff values for the 5 levels of fire danger
adjective rating: low, moderate, high, very high, and extreme.
- Each afternoon Fire Weather Forecasters from the National
Weather Service use WIMS to view the local fire weather
observations and issue trend forecasts for fire weather forecast
zones. WIMS processes these forecasts into next-day index
forecasts.
- WFAS queries WIMS each afternoon and generates maps for
observed and forecasted weather, fuel moisture, and fire danger.
Because trend forecasts are generally issued only during the peak
of the fire season, many areas of the country will not have
forecast information. The result can be large data gaps and
unrealistic interpolations.
- Reporting station locations are indicated with a marker on the
maps. Values between stations are estimated with an inverse
distance-squared technique on a 10-km grid. This works pretty well
in areas of relatively high station density, but has obvious
shortcomings in other areas. Station location is based on the
latitude/longitude cataloged by local station managers in
WIMS.
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