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Heat wave melts Mount St. Helens snowpack, sets temperature records

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Mount St. Helens snow melt

Snow melts on Mount St. Helens in late June.

Last week’s heat wave melted all the remaining snow on Mount St. Helens in short order.

The USDA Natural Resources Conservation Service gathers data about snow and rain from four sensors on Mount St. Helens and dozens more across Washington. Swift Creek, the highest elevation site on St. Helens, recorded 31 inches of snow depth June 25. By July 1 the snow had completely melted.

Scott Pattee is a water supply specialist for the conservation service’s Washington branch. Pattee said it was typical for the mountain’s snowpack to finish melting around the end of June. The monitoring sites at June Lake and Sheep Canyon had lost their snow earlier in the month.

This year’s high elevation snow had been expected to stick around for longer, however, as the mountain saw high accumulation during the winter and cool temperatures throughout most of the spring.

“The melt curve was definitely more rapid. We would have expected that to last at least another week,” Pattee said.

The temperature swing on the mountain represented a greater aberration than the melt. The Swift Creek site hit 90 degrees Fahrenheit on June 29, the highest temperature seen at the station since 2005. While the heat wave set a recent record, Swift Creek had recorded temperatures above 105 degrees multiple times in the early 2000s.

Two other sites on the mountain set all-time temperature records Monday, with Spirit Lake reaching 85 degrees and Sheep Canyon reaching 94 degrees. The site at June Lake reached 95 degrees that day, one degree below the record high from 1988.

The melt released around 20 inches of snow-water equivalent from the mountain, which measures how much water is created by the melt. Pattee said the melting had not been sudden enough to cause flooding, but nearby reservoirs may have needed to adjust their levels to handle the excess water.

The U.S. Geological Survey monitors water flow on Mount St. Helens and across the region through the Cascades Volcano Observatory. Outreach specialist Carolyn Driedger said the melt had caused a spike in water discharge, and a serious spike in the amount of sediment being carried into the rivers, but did not lead to any unexpected issues.

“This heat was felt by humans a lot, but for the landscape it was not so dramatic a change,” Driedger said.

Pattee told KIRO 7 News earlier this week that the speed of the snowmelt on Mount Rainier, and in other parts of the Cascades, could set records once the data is fully evaluated but should only cause short-term issues.


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