Friday, May 7, 2010


Late April's cool, moist weather held off the snow melt and even added to the mountain snowpack according to the latest snow survey conducted by the Natural Resources Conservation Service at the end of April. The spring precipitation boosted the water supply outlook but did not solve the moisture deficit problem which has plagued Idaho all winter.

"If the cool and wet conditions has not occurred in April, snowpacks across the board would have melted out much earlier," said Ron Abramovich, Water Supply Specialist for NRCS. "Rivers would have peaked too soon."

"Most of Idaho's irrigators should be able to make it through this season. Some surface water shortages are likely in central and southern Idaho basins including the Big Wood, Big Lost, Little Lost, Oakley and Salmon Falls and for users that rely on natural streamflow levels," Abramovich added.

April precipitation was above average across nearly the whole state. Monthly precipitation ranged from 94% of average in the Big Lost basin to 140% at the Upper Snake River headwaters and the Bear River drainage.

Current snowpack levels across the state are a mixed bag - anywhere from 45% to 85% of average. The low-elevation snowpack in some places was already melted by mid-April. Snow melt in the higher elevations started in early April but cool temperatures combined with precipitation temporarily halted the melt and even added water content to the snowpack.

The wet, cool weather is helping to refill reservoirs and delay irrigation demand, but not all reservoirs will fill. Of Idaho's 28 major storage facilities, 22 are reporting average or better storage for April 30, and 11 of them are nearly full.

There is still enough snow in the central, northern and upper Snake basins to produce another streamflow peak.

"Reservoir operators are hoping the peak streamflows occur when they normally do in the latter half of May," said Abramovich. "That way they can maximize water storage and delivery for all the various users and uses." For information on specific reservoirs, please refer to the May Water Supply Outlook Report posted online.

April streamflow volumes varied across the state from near average runoff volumes to only half of average. The streamflow forecast for the May-July period remains low with volumes ranging from 45-75% of average.

Timely rains over the next two months would improve this year's water supply. "Additional precipitation and cool temperatures this spring can make working the fields difficult but will help stretch the limited water supplies," Abramovich said.

For the complete May Idaho Water Supply Outlook Report, visit and click on the 'Water Supply' link.

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