At a Wednesday meeting in Powell hosted by the Bureau of Reclamation, Williams said the bureau is expecting 715,800 acre feet of inflow for the October 2012 through September 2013 water year. The minimum listed on a table he provided was 528,300 acre feet.
The average is 847,500 acre feet based on a mean between 1983 and 2012, according to data tables from the bureau.
The reservoir’s expected outflow for the water year is 718,000 acre feet with a minimum of 643,000 acre feet.
Outflow this winter has been 200 cubic feet per second, according to the tables.
Inflow forecast for the April through July period in 2013 is 550,000 acre feet. The minimum is 400,000 acre feet, according to the tables.
Buffalo Bill Reservoir’s average inflow for the April through July period is 668,500 acre feet. In 2011, it was 1.23 million acre feet. In 2012 it was 591,700 acre feet, according to the tables.
“The precipitation we get in the next two months will really tell the tale,” Williams said.
On Sept. 30, the reservoir’s pool elevation was 5,367.3 feet, or 448,858 acre feet of water.
On March 11 Buffalo Bill Reservoir was 66 percent full, with a pool elevation of 5,364.6 or 429,793 acre feet of water — down 2.7 feet elevation or 19,065 acre feet from Sept. 30, according to the tables.
During fall 2011 and early spring 2012, inflow and outflow were average to above average, Williams said.
Last year brought a warm and dry summer, precipitating a greater demand on water, Williams said.
The National Oceanic and Atmospheric Administration’s April through June outlook predicts no strong trends toward above, normal or below normal temperatures in northwest Wyoming, Williams said. The outlook also predicted below-average precipitation for this part of the state.
The March 11 snow report from the Natural Resources Conservation Service showed 91 percent snow water equivalent in the Shoshone River basin, compared to 94 percent on both March 4 and Feb. 25.
That suggests snowpack is not growing in Shoshone River drainages, Williams said.
The state average snow water equivalent was 83 percent March 11.
“Statewide, this is one of the better basins for snow at this time,” Williams said.
The Shoshone River drainage system encompasses 600 square miles, Williams said.
A table logging the last 32 years of inflow illustrates seven years of average inflow during the April through July period. Precipitation was above average during 10 years and below average the other years, including 2012 and the 2013 prediction.
High or low years bring the average up or down. Every year, the average is re-calculated.
“Average ... does vary from year to year,” Williams said.