Spring water levels could mean dry summer statewide
By Ann McCreary
April produced record high temperatures throughout the entire Pacific Northwest, causing much of the remaining snowpack to melt and run off, according to the Natural Resources Conservation Service (NRCS).
Over 80 percent of all SNOTEL (snowpack measurement) sites with at least 15 years of data set new melt rate records for April, said Scott Pattee, NRCS water supply specialist.
During two separate high-pressure weather systems in April, SNOTEL sites experienced minimum daily temperatures exceeding 20 degrees above normal. Due to the rapid snowmelt, runoff was above normal and Washington’s rivers and streams were able to contain it without flooding.
The Methow River streamflows, measured at Pateros, were 443 percent of normal for the month of April, Pattee said. As of May 10, the Methow River was running at 324 percent of normal for that date, at 10,600 cubic feet per second. Although high, “it’s not record flows,” Pattee said.
The Methow River streamflow forecast for May-September is 101 percent of average. But the rapid snowmelt could mean a dry summer, Pattee said.
“I’m still worried about late summer flows since it’s coming off so fast and early,” he said.
While the rapid runoff did not result in significant flooding in the state, many Methow Valley residents have had to cope with standing and running water that has caused damage and made roads impassable at times. Pattee said that is likely a result of the high water volumes coming out of the mountains.
“That basin is so porous. When you raise the river level the water table is going to come up. Everything is so connected hydraulically,” Pattee said.
Some good news
Precipitation in April was much below normal statewide, and that was probably good news in light of the rapid snowmelt, Pattee said.
“Our river basins are ancient, developed over the years so they’re built to handle these flows. But if you added a bunch of rain to it, you’d see flooding,” he said.
Snowpack measurements at the Harts Pass SNOTEL site was 95 percent of normal on May 1, but as of May 10 it had dropped to 76 percent of normal, Pattee said.
“The latest National Weather Service short-term forecasts are calling for warmer than normal with some chance of seasonal precipitation,” Pattee said. “Long-range forecasts for the early summer continue to be warmer than normal with equal chances of precipitation.”
Normal rainfall during this period is only about 13 percent of the annual total, Pattee said. “The leading climate factor this summer will be temperature,” he said.
The May 1 statewide SNOTEL readings were 87 percent of normal. A SNOTEL site near Mt. Adams had the highest percent age with 121 percent. Most basins reported considerable decreases from last month.
Most areas reached peak snowpack by April 1 or before which is two to three weeks early. Snowpack along the east slopes of the Cascade Mountains included the Yakima area with 72 percent and the Wenatchee area with 74 percent. Snowpack in the Spokane River Basin was mostly melted out and the Walla Walla River Basin had 76 percent remaining.
However, year-to-date statewide SNOTEL averages remain above normal at 124 percent.