Sunday/Monday (Aug. 26/27) fire danger to increase

Both the NAM and the GFS (weather prediction models) are showing hot, dry, and windy conditions developing over southwestern SD on Sunday, August 25. Furthermore, the GFS is again painting hot, dry, and windy conditions for Monday over the same area while the NAM model keeps those conditions farther south in Nebraska.

Custer and Fall River Counties (circled below) have not seen the precipitation over the past 7 days that the surrounding areas have seen. The Red Canyon RAWS and the Wind Cave/Elk Mountain RAWS have each reported a scant 0.02" of rain during this period. We are not expecting widespread rain over these areas today or tomorrow and therefore we anticipate the fuels will continue to dry.

Sunday:
Critical fire weather conditions may develop over southwestern SD on Sunday. If the forecast holds, expect a local enhancement in the fire danger, especially over Custer and Fall River Counties where a recent dry spell has been seen. Look for temperatures in the 90, min RH < 20%, and southwest winds gusting from 25-35 mph. A few thunderstorms are possible over central/northern SD but will not likely co-locate with areas of critical fire weather. All of western SD will be hot and relatively dry, but the wind looks to be strongest over those noted southwestern areas.

Monday:
Critical fire weather conditions may continue through Monday for southwestern SD; however, high uncertainty remains in the forecast. The primary uncertainty is in the timing of a frontal passage on Monday; if the front arrives earlier, more humid conditions will occur. However, if the front arrives later (like the GFS model is predicting), the dry, hot, and windy conditions (similar to Sunday's weather) will spread across southwestern SD. And one last notable point: with the front comes the potential for scattered thunderstorms which may imply lightning and ignitions.

Land and fire managers will need to keep an eye on the forecast to see how the situation unfolds.

GFDI possibilities:
Let's look at a couple of different possible weather scenarios and the associated Grassland Fire Danger Indices.

1. A temperature of 93, an RH of 20%, winds of 25 mph, and a curing percentage of 80% yields a Grassland Fire Danger Index of "Very High."
2. A temperature of 96, an RH of 15%, winds of 30 mph, and a curing percentage of 90% yields a Grassland Fire Danger Index of "Extreme."