Summer streamflow forecasts for the Big and Little Wood rivers—already predicted to be significantly below normal this year—are getting even worse.
An unseasonably warm and dry March decreased snowpacks throughout Idaho and has caused summer streamflow forecasts to be reduced statewide from figures released just a month ago, states an Idaho Water Supply Outlook Report from the Natural Resources Conservation Service.
"We actually lost snowpack in the month of March," Ron Abramovich, an NRCS hydrologist, said Tuesday.
This is significant because March is normally a gaining month for snowpack depths, Abramovich said.
On March 1, streamflow predictions for the Big Wood River were calling for a 78 percent of average runoff between April 1 through July 1. But because March precipitation in Idaho's central mountains was only 40 percent of average, that projection has been downgraded to a 53 percent of average runoff prediction, Abramovich said.
As a recent comparison, streamflows in the Big Wood River from April 1 through July 1 of 2006 measured a whopping 200 percent of average, he noted.
According to the NRCS report, there is little possibility for a near normal runoff season unless the months of April and May bring extremely wet and cold conditions.
"Dry conditions removed almost all hopes for a near normal runoff season," NRCS hydrologist Phil Morrisey said.
The only bright spot in the statewide picture is the fact that carryover storage in Idaho reservoirs is generally high due to the above average snowfall the state experienced during the 2005-2006 winter.
Carryover storage in the Magic Reservoir is at its highest level since April 1, 1998, Abramovich said. But another winter like this year's would entirely eliminate that advantage.
"Most of the reservoir storage will be depleted by summer's end across southern Idaho," he said.
The dire predictions for the 2007 water year are based on statewide snowpack figures that have been declining across Idaho since January.
Close to home, the overall Big Wood Basin snowpack was at a discouraging 47 percent of average reading at noon on Tuesday. This is down from a 71 percent of average measurement on Jan. 31, after a promising start to the winter during the months of November and December.
In the Little Wood Basin things are even more dismal, with only a 26 percent of average snowpack as of Tuesday. This figure—down from a 51 percent of average measurement as recently as March 22—places the Little Wood Basin at the very bottom of Idaho river basins. Only the Owyhee River Basin in southwest Idaho is even close, with a 27 percent of average snowpack on Tuesday.
The National Resource Conservation District manages 83 snow telemetry sites throughout Idaho, including nine in the Big Wood Basin. The "snotel" sites are basically remote weather stations that provide automated data on precipitation, snow depth and temperature.
Statewide, the basin with the highest snowpack percentage continues to be the Panhandle Region, with 79 percent of average on Tuesday.
Based on the National Weather Service forecast for the next seven days, weather in the Ketchum area will likely range from mostly clear to partly cloudy skies. The forecast doesn't call for any precipitation.
According to streamflow forecasts for the Big Wood River, shown here at the Croy Canyon Bridge in Hailey, runoff from April 1 through July 1 of 2007 will be just 53 percent of average. Well below average rainfall in March led to a decrease in Big Wood Basin snowpacks, which in turn has led to the dreary streamflow projections. Photo by David N. Seelig
