The hazard will remain HIGH while the storm continues. If you heading into the mountains, use a very conservative approach and avoid avalanche terrain.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
A series of Pacific storms will continue to impact the region for the next few days. On Sunday overnight and Monday, another 15-30cm of snowfall is expected. Freezing levels are forecast to be around 1500m and alpine winds are expected to be strong from the SW. Another storm system is expected for Tuesday. 15-30cm is possible on Tuesday but freezing levels are forecast to climb as high as 1800m. Alpine winds should remain strong from the SW. On Wednesday, another storm pulse is expected with freezing levels dropping back to around 1500m.
Avalanche Summary
Observations have been limited during the storm. On Friday, a natural size 3.5 was reported from a steep NE aspect at 2100m. This was a wind loaded start zone and the slab was 60cm thick. Ski cutting also produced a size 1 storm slab with a 50cm thick slab. On Saturday. several natural size 1 avalanches were reported from below treeline elevation. On Monday, touchy storms slab will continue to be very sensitive to human-triggering at all elevations, especially on steep, convex features. Widespread natural avalanche activity is also expected.
Snowpack Summary
The new overnight snowfall will fall on top of around 50-80cm of recent storm snow. This storm slab sits over a variety of old surfaces including wind-stripped north aspects, hard wind slabs, facets, sun crusts and/or large-sized surface hoar. Of most immediate concern is a crust/surface hoar interface that is highly reactive. Reports suggest that the surface hoar exists as high as 2000m. Strong SW winds are creating thick wind slabs in leeward features at alpine and treeline elevations. Deeper in the snowpack, surface hoar interfaces that were key players in November have been dormant but still may wake up with heavy loading or smaller avalanches stepping down. On very high northern aspects, a crust/facet interface may be found near the ground.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.