As of Thursday, June 2, 2016
What a difference a month makes, according to the Natural Resources Conservation Service (NRCS). Near normal snowpack covered the majority of Idaho, and the NRCS monitoring region, at the beginning of April. The beginning of May, however, tells a much different story. Snow across much of the state has melted at a record high rate during April.
April precipitation across the state covered the extremes: from well-below to well-above average depending on location. Most areas received below average monthly precipitation.
“Precipitation amounts received since the start of the water year on Oct. 1, 2015, remains encouraging with the whole state reporting 92 percent of average or better,” said Ron Abramovich, NRCS water supply specialist. “However, those areas with deficits are worth watching and may not improve much as we move into our dry summer months.”
April precipitation in the Clearwater Basin as a whole was 65 percent of average, according to the NRCS report. However, strong precipitation numbers from December, February and March mean that water year-to-date precipitation totals are still at or above average across the region, ranging from a high of 110 percent of average in the Lochsa to a low of 101 percent for the Selway, while the Clearwater Basin as a whole is 103 percent.
According to NRCS, throughout April the daily mean temperatures in the upper portions of the Clearwater were 7-10 degrees Fahrenheit above the 1981-2010 averages, which resulted in substantial snowmelt at many sites during April. The Clearwater basin as a whole started April with 102 percent of median snowpack, and left the month at 78 percent. This substantial reduction was observed in all sub-basins, with the North Fork of the Clearwater losing 23 percentage points to start May at 81 percent of median, while the Lochsa dropped from 101 percent (April 1) to 66 percent (May 1), and the Selway lost 34 percent points to start May at 70 percent of median snowpack. The substantial melt bumped streamflow up, with the Clearwater having approximately 150 percent of its average April flow volume, while the Lochsa and Selway had 160-170 percent.
The early and quick start of the runoff season means that some of this summer’s water is now “under the bridge” so to speak, stated the report. As a result, forecasted May-July and May-September streamflow volumes are substantially lower (as a percentage of the average) than the forecasts issued on April 1. The forecasts for the Lochsa (76 percent and the Selway (76 percent), dropped roughly 25 percent from the previous Water Supply Outlook Report.