Hazard continues to increase as new snowfall progressively builds storm slabs. If you heading into the mountains, use a conservative approach and assess the local conditions before committing to any avalanche terrain.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
A series of storm systems will continue to impact the region during the forecast period. The next storm front should arrive late Saturday afternoon or early evening and is expected to yield 10-20cm of snow by Sunday evening. Snowfall amounts are expected to be greatest towards the north of the region. Freezing levels are expected to be 1000-1400m during this period with strong SW winds in the alpine. On Sunday overnight and Monday, another 15-20cm of snow is possible in the highest snowfall areas. Winds will continue to be moderate to strong from the SW and freezing levels should be around 1500m or lower. On Tuesday, similar amounts of precipitation are being forecast but freezing levels could rise to 2000m or higher.
Avalanche Summary
On Saturday, explosives triggered a size 2.5 deep persistent slab avalanche in the Dogtooth. This was triggered in a steep, rocky, and unsupported terrain feature and released on the crust/facet interface on the ground. Other explosives resulted in thin wind slabs releasing. If enough snow falls Saturday night, the storm problems may become more widespread. In the deepest western parts of the region (Bugaboos/Bobbie Burns areas), the hazard may be higher if the storm slabs exceed 30-40cm thickness.
Snowpack Summary
The new overnight snowfall will fall on top of around 10-20cm 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 already super-reactive. Reports suggest that the surface hoar exists as high as 2000m and the crust may be found on all aspects. I would not rule out the possibility of weak interfaces at higher elevations, especially sun crusts and facets. 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.