Friday 2/21/20 - Thursday 2/27/20
This week on As the World Terns:
High pressure has been the dominant force of late with the exception of a storm Sunday to Monday. This system favored the Swan Range with 2” of SWE and 20” of snow. At times the rate of snowfall reached 1” per hour resulting in rapid loading of the snowpack. The new snow refreshed alpine fetches and fed moderate-strong winds enough substrate to continue wind slab and cornice growth. Sluffing occurred in steep terrain especially where the old snow surface was crusted. However, the trickiest hazard formed where storm snow buried well-preserved surface hoar. This weak layer formed during the calm and clear conditions last week. It appears that the sun cooked off surface hoar on solar aspects and Saturday’s wind blasted it to pieces in exposed terrain. Observers noted cracking, collapsing, propagating pit results, and recent avalanche activity on Northeast aspects near Noisy Basin and the Southern Whitefish Range. All of these instabilities were attributed to buried surface hoar. As of now we have no evidence that this layer persists in the Flathead Range which received a more thorough raking by the pre-storm winds. Where it is present, this layer may linger for awhile. Treat sheltered areas with care: dig in the snow and let us know what you find.
Forecast Hotline: 406.257.8402
Call or text an observation: 406.66AVYOB