Upper Snake River Basins February 1, 2016 WATER SUPPLY OUTLOOK

 Precipitation across the Upper Snake River basins showed substantial variability with Pacific Creek
(in the north) receiving only 73% of typical January values, while in the south the Salt and Portneuf
rivers both reported 120%. For the water year to date, precipitation values range from a low of 86%
(Hoback River) to a high of 112% (Portneuf), while the Snake River above American Falls is right on
target at 98% of average. Snowpack numbers across the Upper Snake are very good overall, ranging
from a low of 91% of median snowpack (Hoback and Gros Ventre rivers) to a high 114% in the
Portneuf drainage, while many basins are reporting snowpack percentages within 5% of median.
Looking at the Upper Snake as a whole, the Snake River above American Falls has 98% of median
snowpack. In most cases reservoir levels in the Upper Snake are trailing slightly behind where they
were at this time last year, but are still near or above average for the end of January. Jackson Lake
and Palisades are at 131% and 87% of average, while their combined storage is at 101% of average
for the end of January. Taken as a group, Henrys Lake, Island Park Reservoir, and Grassy Lake have
a combined storage of 187 KAF, which is 97% of average. Moving downstream, Blackfoot and
American Falls reservoirs are at 98% and 82% of average values.
Projected streamflow volumes in the Upper Snake range from a low of 85% of average for Willow
Creek to a high of 107% for the Portneuf River. However, most basins are projected to have
approximately 90-95% of average flows, with the Snake at Irwin, Heise, and Neeley all forecast at
90% of average.