Despite positive snowfall last winter across much of Idaho, tight water supplies are anticipated in the Big and Little Wood river basins.
The ample snowfall that fell across many of the state's river basins and the cool spring temperatures that helped retain high country snowpacks came as a relief to the state's water managers, farmers and recreational boaters. However, the U.S. Natural Resources Conservation Service's May 1 Water Supply Outlook Report for Idaho indicates that precipitation for the past few months was below normal in most river basins.
April temperatures were 6-10 degrees below normal in the Pacific Northwest and northern Rocky Mountains. That added more snowfall in higher elevations and preserved snowpack accumulations into May. Early April is traditionally when Idaho's snowpacks are at their highest before melting and heading downstream, the agency said.
But April precipitation ranged from 90 percent of average in the Clearwater and Panhandle regions to 40 percent in the Big Wood, Little Wood and Big Lost basins. Across central Idaho, which includes the Salmon, Weiser, Payette, Boise and Big and Little Wood river basins, April was the third consecutive month of below-normal precipitation.
The cool weather meant snowpacks just reached their peaks at the end of April in the Panhandle, Clearwater, Salmon, Payette, Henry's Fork, Teton and Upper Snake basins. The highest snowpacks remain along the west side of the state, from the Weiser River basin at 168 percent of average to the Kootenai River basin at 121 percent. Snowpacks are at 140-160 percent of average in the Coeur d'Alene, Spokane, North Fork Clearwater, Lochsa and Selway river basins. To the south, the snowpack in the Salmon River basin is at 120 percent.
Closer to home, the Boise and Little Wood river basins are about 115 percent of average, while the Big Wood basin is at 106 percent. Snowpacks decrease to near-normal levels in the Big Lost and Little Lost river basins.
According to the Conservation Service, most reservoirs in the state are at 50 percent to 80 percent of capacity and are maintaining storage space for the snowmelt runoff. Whether reservoirs fill completely may come down to timing of runoff and irrigation demand.
