Upper Missouri Basin
The high elevation snow pack in the Upper Missouri Basin as of
May 1 was below average. The snow pack above Toston, Montana
was 64 percent of average. The snow pack between Toston and Fort
Peck, Montana was 65 percent. The snow pack in the St Mary and
Milk river basins was 75 percent.
April precipitation was above average across most of the Upper Missouri
Basin. The Milk St. Mary was near average. Basin precipitation
summaries for the Missouri Basin include: Milk St. Mary, 87 percent;
Milk Canada, 190 percent; Lower Milk, 158 percent; Above Toston,
101 percent; Toston to Ft. Peck, 142 percent.
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 88 percent of average May-September flows. Runoff is expected to
range around 68 percent of average for the Missouri Basin above Fort
Peck, Montana. Forecasts for the Milk River Basin call for around 80
percent of average spring summer runoff.
Of the four major irrigation reservoirs in Montana: Lima Reservoir
had 138 percent average storage, Clark Canyon was holding 82 percent of
average water, Gibson Reservoir had 124 percent of average stored
water, and Fresno Reservoir had 102 percent of average stored water.
The major hydroelectric reservoirs in Montana (Canyon Ferry and
Fort Peck) had monthend storage in the average to below average
range; 108 and 57 percent of average water, respectively.
As indicated by the U.S. Geological long term gaging stations,
the Marias River near Shelby, Montana had an estimated 73 percent
of average runoff in April.
The high elevation snow pack in the Yellowstone Basin was mostly
below average on May 1. The snow pack in the Upper Yellowstone
Basin was 64 percent of average. The snow packs in the Wind,
Bighorn, and Shoshone Basins were 54, 67, and 56 percent of
average, respectively. The snow packs in the Tongue and Powder
basins were 84 and 70 percent of average, respectively.
Precipitation during the month of April was about 33 percent of
average in the Wind River Basin above Boysen Reservoir, 98 percent
of average in the Bighorn Basin, 126 percent of average in the
Upper Yellowstone Basin, 71 percent of average in the Little
Bighorn Basin 52 percent of average in the Powder Basins, and
209 percent of average in the lower Yellowstone Basin.
Stream flow in the Yellowstone Basin is forecast to be average to
below average during the upcoming spring and summer. Runoff at
Billings, Montana is expected to be 81 percent of average, with
a probable range between 54 and 107 percent of average. Stream
flow for the Wind-Bighorn Basin above St. Xavier, Montana is
forecast to be 51 to 54 percent of average with a probable range
of 25 to 80 percent of average flow in sub-basins. Flow in the
Tongue Basin is expected to be 88 to 90 percent of average with
a reasonably likely range of 49 to 128 percent of average flow.
Flows in the Powder River are expected to be about 65 percent of
average with a reasonably likely range of 12 to 117 percent.
Monthend storage was at 80 percent of average at Boysen Reservoir
in Wyoming, 140 percent of average at Buffalo Bill Reservoir in
Wyoming, and 101 percent of average at Bighorn Reservoir on the
Runoff during April in the Yellowstone River was 128 percent
of the 1971 to 2000 average at Corwin Springs, Montana and 97
percent of that average at Billings, Montana.
Platte BasinThe high elevation snow pack in the Upper North Platte basin was
62 percent of average. The snow pack in the North Platte Basin
below Seminoe Reservoir was 61 percent of average. The snow pack
in the South Platte Basin was 101 percent.
Precipitation across the Platte Basin was below average to above
average for the month of April. Precipitation in North Platte Basin
above Seminoe Reservoir was 64 percent average. In the North
Platte Basin between Seminoe Reservoir and Guernsy Reservoir
precipitation was 66 percent of average. The North Platte Basin below
Guernsy Reservoir had 100 percent of average precipitation. The high
elevations of the South Platte Basin had 103 percent of average
precipitation whereas the plains had 140 percent of average
Stream flow in the Platte basin is forecast to range from below average
to average during the upcoming spring and summer. Runoff for streams
above Seminoe Reservoir are expected to be about 50 to 70 percent of
average. Stream flow for the North Platte below Seminoe Reservoir are
forecast to be between 25 to 80 percent of average. The South Platte
Basin above South Platte, Colorado can expect about between 70 and
115 percent of average flow. For the remainder of the South Platte
Basin flows are expected to be about 100 percent of average.
Stored water in the North Platte Basin as of May 1 was 69
percent of average. The South Platte Basin had 94 percent of
average stored water.
April 2007 Oct-Apr WY 2007