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Fire Weather Forecast Parameter Definitions


Parameter
Definition
Sky/Weather Cloud cover (% of sky covered) and weather phenomena forecast during the period.
Areal Coverage Descriptions:
Isolated = less than 15%
Widely Scattered = 15-24%
Scattered = 25-54%
Numerous/Widespread = 55-100%
Max Temperature The highest temperatures (°F) expected during the forecast period.
Min Temperatures The loweest temperatures (°F) expected during the forecast period.
Max Humidity The highest relative humidity (%) expected during the forecast period.
Min Humidity The lowest relative humidity (%) expected during the forecast period.
20-Foot Wind The average 10-minute wind speed (mph) and direction 20-feet above the vegetation.
Ridge Top Wind The average 10-minute wind speed (mph) and direction 20-feet above the local higher terrain (hill, butte, peak, etc.).
LAL Lightning Activity Level:
1 - No Thunderstorms
2 - Isolated Thunderstorms - single cell, LT 20 strikes/hour, LT 20 total strikes.
3 - Widely Scattered Thunderstorms - up to 70 strikes/hour, 20-40 total strikes
4 - Scattered Thunderstorms - 25-130 strikes/hour, 40-80 total strikes
5 - Widespread, numerous Thunderstorms - 75-300 strike/hour, 80-160 total strikes.
6 - Dry Lightning Outbreak - generally high-based dry thunderstorms, at least widely scattered in coverage, up to 70 strikes/hour, up to 40 total strikes.
Chc of Wetting Rain The chance of rainfall exceeding 0.10 inches.
Transport Wind Average wind speed (mph) and direction in the mixing layer (surface to mixing height).
Mixing Height Depth of the mixing layer (feet above ground level).
Smoke Dispersal Excellent - 150,000 knot-feet and greater
Very Good - 100,000 to 149,999 kt-ft
Good - 60,000 to 99,999 kt-ft
Fair - 40,000 to 59,999 kt-ft
Poor - Less than 40,000 kt-ft
Haines Index Lower Atmospheric Stability Index. The potential for the growth of large, plume-dominated fires. Scale ranges from 2 (very low) to 6 (high). High level Haines is used in WFO Riverton products.

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