Supply Forecast Program Monitors Mount Saint Helens Snowpack 

Spirit Lake SNOTEL site in the state of Washington -  photo by Melissa Clark

In the interest of public safety, the National Weather Service Northwest River Forecast Center has requested the NRCS Snow Survey and Water Supply Program to resurrect a procedure developed in May 1980 to estimate snowpack water content surrounding Mount Saint Helens.

After several decades of inactivity, Mount Saint Helens erupted in late September 2004 with ash and steam coming from the crater dome. A series of harmonic tremors also signaled the movement of lava upward into the crater and brought concern that an eruption, and subsequent rapid snowmelt, could once again flood the Toutle River valley.

Immediately following the 1980 eruption, the NRCS installed additional Snow Telemetry (SNOWTEL) sites near Mount Saint Helens to monitor seasonal snowpacks. Six SNOTEL sites still surround the mountain and provide observations every six hours that are placed on the Oregon Snow Survey and Water Supply Forecasting Program webpage.  The six SNOTEL sites are used to create a weekly Mount Saint Helens Snowpack Analysis. The Snowpack Report summarizes the amount of water available from existing snowpacks in four quadrants, (north, south, east, west) that surround the mountain. Area-elevation curves constructed in 1980 are used to estimate the volume of water, in acre-feet, for each quadrant in three vertical zones (3,330 to 4,101 ft., 4,100 to 4,900 ft., and 4,900 to 8,200 ft.). The water content can be used as input to flood routing models that estimate peak flows and travel times to downstream points.

Cascade Mountain snowpacks generally peak in early April and by July most snowpack has melted except for high elevation glaciers which were significantly reduced in size when the mountain lost 1,314 feet during the 1980 eruption. The post-1980 Mount Saint Helens landscape is greatly diminished in its ability to capture and retain significant snowpacks on the north face which collapsed and blew outward into Spirit Lake. Inside the crater, a glacier has formed between the lava dome and the south side of the crater. The USGS estimates this glacier contains 43,240 acre-feet of water that is affected by strength of eruptive activities within the dome. The National Weather Service includes this volume with the north quadrant snowpack to determine flood risk. The USGS Cascades Volcano Observatory provides a wide variety of information describing Cascade Volcano seismic activity.
Your contact is Jon Werner, Acting Director, NRCS National Water and Climate Center, at 202-720-0772, or jon.werner@usda.gov