Major warming and sun are expected to destabilize the snowpack over the weekend. Wind slabs are expected to remain reactive, cornices will continue to weaken, and deep weak layers may begin to wake up. Wet loose activity should be expected on steep sun exposed slopes.
Wind slabs are may remain reactive on Sunday, especially on shady aspects and where they overlie a crust. Cornices will also continue to weaken with warming through the weekend.
Wet loose avalanches will become possible at all elevations with warming this weekend. Extra caution is necessary around steep south facing slopes when the sun is strong.
An old persistent weak layer buried deeply in the snowpack has been dormant recently but will get tested this weekend with the sustained warming event. Cornice falls or smaller avalanches have the highest potential to step down to a deeply buried weak layer.
The region now sits under the warm ridge of high pressure which is expected to persist into next week bringing very high freezing levels and sun.
Saturday night: Partly cloudy, light W wind, freezing level 2800 m with an inversion.
Sunday: A mix of sun and cloud, light W wind, freezing levels around 2500 m with an inversion, dropping to around 2200 m by Sunday night.
Monday: Sunny, light NW wind, freezing levels around 2700 m with an inversion.
Tuesday: A mix of sun and cloud, light NW wind, freezing levels around 2700 m with an inversion.
On Friday, natural and skier triggered wind slabs size 1.5-2 were observed and explosive control work produced size 2 cornices. Small solar triggered loose wet avalanches were observed on steep south facing terrain. On Thursday, a few natural wet loose avalanches size 1-2 were observed at treeline and below during the storm as well as some small loose dry at higher elevations. Ski cutting triggered a couple storm slabs size 1-1.5 and explosives triggered several size 2 storm slabs and cornices. The storm slabs appear to typically be 20-30 cm thick but up to 50 cm in loaded terrain.
Last week, a very large natural avalanche cycle took out mature timber and left mountainous piles of debris down to very low elevations. Check out the insane photos of the size 4 in this MIN from January 15th. Avalanches of this scale wouldn't be surprising during the current warm weather. Parts of the region are currently under a Special Public Avalanche Warning (SPAW). Check out this new blog post for additional information.
At higher elevations, 15-30 cm of recent storm snow has buried the widespread January 16 melt-freeze crust which extends to around 2100 m. There have also been some observations of surface hoar sitting on the crust on polar aspects at treeline and in the alpine north of Pemberton but this does not appear to be widespread. The most recent storm snow has formed reactive wind slabs in exposed high elevation terrain. At lower elevations, the upper snowpack is moist or wet from the recent rain event.
The depth of the early December crust/facet layer is highly variable through the region but appears to be typically down 100-200 cm. Some operators are showing the depth as low as 60 cm in shallow snowpack areas and as deep as 3 m in wind loaded terrain. The weak layer is most prominent between 1700 and 2100 m. The layer has been dormant recently but is a concern for the period of major warming and sun forecast over the weekend. The most likely place to trigger it would be in thin, rocky snowpack areas where it is shallowest.
