The mountain snowpack has improved after a dry start to the year, but questions remain about spring runoff because soils were so dry going into winter.
Updated readings are down from earlier in the year
Even with a snowy first week of March, it’s hard for snow to compete with the warmer temperatures of late winter.
Although parts of the valley received a considerable amount of snow — Mazama got more than 15 inches in the first 10 days of March, and Winthrop got more than 4 inches — the new snow added just 5 inches to the snow depth in Mazama and 1 inch in Winthrop, according to National Weather Service data.
There have been small storms in the mountains, but nothing significant, said Scott Pattee, water supply specialist at the Washington Snow Survey Office of the Natural Resources Conservation Service. “This time of year, every day without snow, you lose ground,” he said.
In early March, Harts Pass received just a few inches of snow, according to Pattee. That continues a trend that started early in this winter, where the valleys often received more precipitation than at higher elevations, Pattee said.
There has been precipitation in both the mountains and lowlands, but “it just hasn’t been enough to keep up with what we should be seeing this time of year, causing greater divergence below normal as we go through time,” Pattee said.
Snowpack in most areas has been diminished by an unusually snow-free February. “Cold and dry conditions gripped most of the state last month. With only a handful of exceptions, monthly precipitation was much below to just near normal,” Pattee said in the Washington Water Supply Outlook Report released on March 1.
Snowpack (or snow-water equivalent) in the Methow basin was at 100% of normal at the beginning of March, slightly better than this time last year. Still, the Methow basin snowpack has been on the decline. It was 109% in January and 104% in February.
On March 1, snowpack in the Upper Columbia basin was 113% of normal, about as high as it’s been all season, Pattee said. But by March 10, it had dropped to 103%.
The snowpack has improved at Harts Pass, reaching 94% of normal, up from the 80s, Pattee said. Harts Pass has the highest Snotel gauge in the state, at 6,500 feet.
Precipitation in the Upper Columbia basin was just 74% of average for February, among the lowest in Washington. For the entire water year, which starts in October, total precipitation there is just 89% of normal, in part because October was exceptionally dry.
By contrast, basins in the Okanogan have received an atypical amount of moisture this winter. Snowpack in the Loup Loup basin is at 147% of normal, and the Omak basin is at 146%, Pattee said. The Snotel gauge for the Omak basin is at 5,010 feet.
Watching soil moisture
Climatologists are carefully monitoring readings for soil moisture, since the season started with soil in record-dry conditions. At the beginning of winter, soil moisture at Harts Pass was 6%, whereas in a typical year fall rains bring it up to 60%, Pattee said.
As a result, the snow at Harts Pass fell on parched soil. As snow starts to melt in the spring, it first soaks into the ground and won’t start flowing into high-mountain streams until the soil has been saturated, Pattee said.
The Methow and Okanogan valleys rely on snowpack to recharge streams and rivers throughout the summer and fall, for household and commercial water use, for agriculture, and for fish.
