Much needed rain on the way

The 104 acre Anada fire burned yesterday, 9/18, roughly 25 miles east of Rapid City. This man-caused fire was started from a combine and burned through 2-ft tall grass and was pushed by a 10-mph wind. Peak temperature were in the mid-70s and the minimum RH was near 40%. These conditions led to flame lengths on the head of the fire of 6-8 ft. The weather conditions were far from critical but the fire behavior showed that the fuels were definitely dry and susceptible to rapid fire spread.

The number of days since the last wetting rain is related to the potential for large grass fires. During September if two or more weeks have passed since the last wetting rain, the potential for prairie fire dramatically increases. And as of yesterday, nearly all West River stations hadn't reported a wetting rain in 20+ days with some stations not seeing a wetting rain in over a month. It had been 18 days, 21 days, and 27 days since the last wetting rains at Rapid City Regional Airport, Ellsworth Air Force Base, and Pinnacles RAWS site, respectively. These are the closest stations to the Anada fire and at least represent the conditions on the ground there.

Luckly, rain is on the way. We've already seen a few hundreths of an inch of drizzle/rain over and south of the I-90 corriodor of western SD. Areas farther north of I-90, west of the Missouri River, have seen from 0.20 to 0.50 inches of rain.

The forecast calls for even more precipitation over the next 36 hours. The convection-resolving HRRR weather model shows more precipitation on the way (image below).

In short, this is good news. However, the forecast for precipitation over far southwestern SD does not look nearly as optimistic. And remember that this is an area that has been quite dry over the past 50 days. Critical conditions are not expected in the near future, but if they do develop, we'll have to watch this area of the state for higher fire potential.