Missouri Basin River Forecast Center
Water Supply Statement
Issued in cooperation with the Natural
Resources Conservation Service
Issued: June 16, 2021
June 1, 2021 Spring and Summer Streamflow Forecasts
Upper Missouri Basin
The high elevation snow pack in the Upper Missouri Basin as of June 1
was near average. The snow pack in the St. Mary Basin was 104 percent.
May precipitation across the Upper Missouri Basin was near average.
Basin precipitation summaries for the Missouri Basin include: Milk St. Mary,
78 percent; Milk Canada, 112 percent; Lower Milk, 107 percent; above Toston,
108 percent; Toston to Ft. Peck, 103 percent.
May 2021 Upper Missouri Mean Precip Oct-May WY2021 Upper Missouri Mean Precip
Stream flow in the Upper Missouri Basin is forecast to be
below average during the upcoming Spring and Summer.
The St. Mary River is forecast to have 83 percent of average
May-September flows. Runoff is expected to range around
95 percent of average for the Missouri Basin above Fort Peck,
Upper Missouri June 1, 2021 Spring and Summer Streamflow Forecasts
Of the four major irrigation reservoirs in Montana; Lima
Reservoir had 102 percent average storage, Clark Canyon was
holding 96 percent of average water, Gibson Reservoir had 92
percent of average stored water, and Fresno Reservoir had
102 percent of average stored water.
The high elevation snow pack in the Yellowstone Basin was near to above
average on June 1. The snow pack in the Upper Yellowstone Basin was 72 percent
of average. The snow packs in the Wind, Bighorn, and Shoshone Basins were 80,
95, and 68 percent of average, respectively. The snow packs in the Tongue
and Powder basins were 116 and 147 percent of average, respectively.
Precipitation during May was below average. The upper Yellowstone
River Basin received 82 percent of average precipitation while the
Lower Yellowstone River Basin reported 81 percent of average. The
Bighorn Basin received 76 percent of average precipitation while the
Wind River Basin received 95 percent of average. The Little Bighorn -
Upper Tongue Basin received 54 percent of average and the Powder River
had 74 percent of average precipitation.
May 2021 Yellowstone Mean Precip Oct-May WY2021 Yellowstone Mean Precip
Forecast stream flow in the Yellowstone Basin is below average
for the upcoming Spring and Summer. Stream flow for the
Yellowstone River above Sidney, Montana is forecast to be about
93 percent of average. Flow in the Tongue Basin is expected to be
108 percent of average. Flows in the Powder River are expected
to be about 72 percent of average.
Monthend storage at Boysen Reservoir was 114 percent of average.
Stored water in Buffalo Bill Reservoir was 120 percent of average.
Monthend storage was 94 percent of average at Bighorn Reservoir.
Yellowstone June 1, 2021 Spring and Summer Streamflow Forecasts
The high elevation snow pack in the Upper North Platte Basin was
66 percent of average on June 1. The snow pack in the North Platte
Basin below Seminoe Reservoir was 68 percent of average. The snow
pack in the South Platte Basin was 112 percent of average.
Precipitation during May in the Upper North Platte Basin was 66
percent of average. In the Lower North Platte Basin, precipitation
was 67 percent of average. The North Platte Plains below Guernsy
Reservoir had 81 percent. The South Platte Mountains had 160
percent whereas the Plains had 161 percent of average May
May 2021 Platte Mean Precip Oct-May WY2021 Platte Mean Precip
Stream flow in the Platte Basin is forecast to be below
average during the upcoming Spring and Summer. Runoff
for streams above Seminoe Reservoir are expected to be
about 75 percent of average. Streams in the South Platte
Basin above South Platte, Colorado can expect 67 percent
of average flow. For the remainder of the South Platte
basin, flows are expected near 83 percent.
Stored water in the South Platte Basin was 110 percent of average
on June 1.
North Platte Streamflow Fcst South Platte Streamflow Fcst