Weekly Summary
February 20th-26th
Crouching Wind Slab, Persistent Dragon. Last weekend saw a string of natural and rider triggered avalanches ranging in size from small to historic that resulted in several near misses, and a partial burial. An Avalanche Warning was issued Monday for all forecast zones as an Atmospheric River brought more than an inch of Snow Water Equivalent (SWE) to the region along with strong southwest winds.
The 7-10” of new snow and strong winds added to large slabs and increased loading of a persistent weak layer now buried 4-6 feet deep, leading to an extended Avalanche Warning in the Swan, Flathead and Glacier NP zones for a second day. Natural and rider triggered avalanches continued. One historically huge avalanche, running down from Heavens Peak, spilling across McDonald Creek and impacting the Going-to-the-Sun road.
Wednesday after a natural, Very Large avalanche traveled over a snow shed in Stevens Canyon, active avalanche mitigation was conducted resulting in several Large to Very Large (D2-D3) avalanches brought down in the surrounding paths. That same day was also a short reprieve from the storms, and we were able to take in some vitamin D.
A series of pulsing storms closed out the week with continued light to moderate snow and wind that brought the Persistent Slab problem back to the forefront. Weak layers associated with the mid-January crust are still alive and well, and can propagate across steep start zones. These layers are now buried 3-6 feet deep and have resulted in avalanches on south and west aspects, not just north and east. The challenge now is not only avoiding certain aspects but also limiting yourself to low angle slopes.
