National Weather Service United States Department of Commerce

Missouri Basin River Forecast Center
Water Supply Statement
Issued in cooperation with the Natural
Resources Conservation Service
Issued:  August 16, 2021


 Upper Missouri Basin

July precipitation across the Upper Missouri Basin was below average. Basin precipitation summaries for the Missouri Basin include: Milk St. Mary, 32 percent; Milk Canada, 47 percent; Lower Milk, 36 percent; above Toston, 54 percent; Toston to Ft. Peck, 43 percent. 

Of the four major irrigation reservoirs in Montana; Lima Reservoir had 52 percent average storage, Clark Canyon was holding 60 percent of average water, Gibson Reservoir had 88 percent of average stored water, and Fresno Reservoir had 26 percent of average stored water.

Yellowstone Basin 

Precipitation during July was below average. The upper Yellowstone River Basin received 56 percent of average precipitation while the Lower Yellowstone River Basin reported 40 percent of average. The Bighorn Basin received 53 percent of average precipitation while the Wind River Basin received 99 percent of average. The Little Bighorn - Upper Tongue Basin received 45 percent of average and the Powder River had 72 percent of average precipitation.

Monthend storage at Boysen Reservoir was 109 percent of average. Stored water in Buffalo Bill Reservoir was 113 percent of average. Monthend storage was 85 percent of average at Bighorn Reservoir.


Platte Basin 

Precipitation during July in the Upper North Platte Basin was 74 percent of average.  In the Lower North Platte Basin, precipitation was 118 percent of average.  The North Platte Plains below Guernsy Reservoir had 35 percent.  The South Platte Mountains had 96 percent whereas the Plains had 62 percent of average July precipitation.

Stored water in the South Platte Basin was 122 percent of average on August 1.


July 2021  WY 2021
July 2021 Precipitation Percent of 1981-2010 Average WY2021 Precipitation as Percent of 1981-2010 Average
July 2021 Basin Mean Precipitation          WY2021 Basin Mean Precipitation
July 2021 MBRFC Basin Mean Precipitation      WY2021 MBRFC Basin Mean Precipitation