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US Forest Service

Fire Applications Support 

WIMS TechNote

Fire and Aviation Management Staff WIMS TechNote-99-01

Date: 15-June-99

System: WIMS

Subject: Multiple changes to NFDR Calc Processor

Purpose: Inform users of correction to add logic for winter observations when fuels are covered with snow by modifying RH range and precipitation duration for snow/fuel interface. Also 10-hr fuel moisture is no longer set to 35 for State of Weather = 4 (fog) or 9 (Thunderstorm).

Contact: Fire and Aviation Management Applications Helpdesk

FS-Mail: fire?/wo,nifc

Internet: fire?/

Phone: 800-253-5559


1. With increasing number of weather stations running year round, the effect of being covered by snow was not being accounted for in the 100 and 1000 hour fuel moisture routines.

2. 10-Hr Fuels were being set to 35 for state of the weather = 4 (fog) and 9 (thunderstorm) on sites where 10-hr stick moistures are not weighed.


1. Add logic for winter observations when fuels are covered by snow by modifing rh ranges and precip duration for fuel/snow interface. Snow cover is assumed if fuels are wet, it is not precipitating at observation time, and it is between November and March. The assumption is further modified by the observed temperature to model thawing as precip duration on the heavy fuels. These local modifications (rh max, rh min, and precip duration) are not updated in the weather observation for the day that is stored in NIFMID.

Code by Larry Bradshaw, Fire Sciences Lab. Missoula. Apr. 1999 Based on GTR PSW-82, Cohen & Deeming, pp 5 & 6.

2. 10 Hour fuel moisture is set to 35 percent only if state of the weather explicitly has widespread precipitation at observation time (drizzle, rain, snow). Wet fuels from fog, rain showers, and thunderstorms must be explicitly set with the fuels wet flag.

Performed by:

Thanks: Larry Bradshaw, Fire Sciences Lab., Missoula, Mt. and Linda Glick, NITC- KC

Changes were made to this page 11/28/06.

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