High temperatures in April caused much of the Pacific Northwest’s mountain snowpack to melt, a federal water expert said.
Runoff was above normal because of the rapid snowmelt, but Washington’s rivers and streams were able to contain it without flooding.
Temperatures were 20 percent above normal during April, eliminating much of the abundant mountain snowpack left over, federal water supply specialist Scott Pattee said.
“Long-range forecasts for the early summer continue to be warmer than normal,” said Pattee, who works for the Natural Resources Conservation Service.
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Precipitation during April was well below normal, and not much additional rain or snow is expected in coming months, he said.
“Normal rainfall during this period is only about 13 percent of the annual total,” Pattee said.
Many parts of Washington depend on a slow melting of the snowpack to provide water during hot summer months. Some recent winters have seen little snow, leading to droughts.
Pattee said the May 1 snowpack readings averaged 87 percent of normal in Washington, down significantly from earlier readings.
The Tolt River Basin reported the lowest readings at 44 percent of the 30-year median among those with remaining snow. Potato Hill near Mt. Adams had the highest reading at 121 percent of normal.
Most river basins reported considerable decreases in snowpack, after reaching peak snowpack by April 1 or before, which is 2-3 weeks early, Pattee said.
Snowpack along the east slopes of the Cascade Range included the Yakima area with 72 percent of normal and the Wenatchee area with 74 percent of normal. The snowpack in this region is heavily used to irrigate farmlands and to reduce wildfires by keeping forests wet.
Snowpack in the Spokane River Basin had mostly melted away, Pattee said.