Purcells

A Special Public Avalanche Warning (SPAW) is in effect for this region. Warming temperatures and strong wind Friday are expected to give way to a natural avalanche cycle. Seek out simple/conservative terrain free of overhead hazard.

Moderate - Freezing levels are uncertain on Friday

THURSDAY NIGHT: Freezing level near valley bottom, light to moderate southwest wind at treeline with strong to extreme southwest wind at ridgetop, 1 to 5 cm of snow.FRIDAY: Scattered cloud cover in the morning, only a few clouds by lunch, freezing level somewhere between 1200 and 2000 m, moderate southwest wind at treeline, strong southwest wind in the alpine, trace of precipitation. 5 to 10 cm of snow above 1000 m Friday evening.SATURDAY: Broken cloud cover giving way to clear skies in the evening, freezing level holding around 1200 m, strong west/southwest wind at all elevations initially, alpine winds stay steady at strong southwest, wind around treeline backing off to light southwest, trace of precipitation. SUNDAY: Scattered cloud cover, freezing level beginning near valley bottom rising to 1500 m, light south wind below treeline, moderate to strong southwest wind in the alpine, no significant precipitation expected.

On Wednesday natural avalanches to size 2 were reported from all aspects and elevations. Control work produced storm slab avalanches to size 2 on a variety of aspects as well. One of the more interesting results was a size 2 avalanche on a northeast facing feature at 2200 m was sensitive to remote (from a distance) triggering. In the neighboring Glacier National Park region natural avalanches to size 3 were reported.

The region picked up 15 to 50 cm of new snow with moderate to strong southwest wind Tuesday through Thursday. This new snow rests on a buried weak layer (December 10th) that consists of facets, surface hoar, and a crust on solar aspects. Results on this interface are quite variable. It's very touchy in some places and less reactive in others.There are two layers of surface hoar (weak feathery crystals) 30 to 70 cm below the surface. The surface hoar is most prominent at treeline, but it may be found in sheltered alpine areas. Both of these layers may be associated with a sun crust on south aspects in some areas.Another major feature in the snowpack is a combination of a crust and faceted (sugary) snow found at or near the base of the snowpack. This layer is most prominent in the alpine.The early season snowpack is highly variable in the Purcells. Total snowpack depths vary greatly throughout the region with anywhere between 70 and 150 cm in the alpine tapering rapidly at treeline and below. In shallow snowpack areas, the bottom half of the snowpack is reportedly weak and "hollow" feeling on shady aspects due to sugary, faceted snow.