There is uncertainty as to the intensity of a storm impacting the region Tuesday into Wednesday. Danger ratings and problems reflect the upper end of forecast precipitation which is concentrated in the south of the region.
Confidence
Low - Forecast snowfall amounts are uncertain on Wednesday
Weather Forecast
WEDNESDAY: Periods of snow Tuesday night into Wednesday, accumulations 10-30cm. Higher amounts concentrated in the south of the region/ wind light to moderate northwest / alpine temperatures -11 THURSDAY: Mainly cloudy with isolated flurries / wind moderate northwest / alpine temperature -9 FRIDAY: Mainly sunny / wind moderate north / alpine temperature -14
Avalanche Summary
Reports from the past 2 days include explosives controlled and natural storm snow avalanches to size 2.5 in the alpine and tree line. There have also been a few reports of skier accidental and skier remote (triggered from a distance) avalanches to size 1.5 at and below tree line. As snow accumulates and settles in the coming days expect to see in human triggered avalanche activity continue even as the latest forecast storm ends.
Snowpack Summary
The 40-70 cm of new snow accumulating through the past 5 days now sits on a wide variety of old surfaces including large surface hoar (weak, feather-like crystals), hard crusts formed by sun or wind, and sugary facets. As the snow load builds and slab properties develop, it will be important to monitor how the new snow is bonding to the old surfaces. Most concerning would be areas that have seen previous surface hoar development, such as sheltered areas at and below tree line and sheltered northerly aspects in the alpine. Additionally, any steep solar aspects where the surface hoar may be sitting on sun crust should be considered areas where this weak layer may be very likely to trigger.A crust which was formed by rain in late November is a major feature in the snowpack and is down approximately 70-100cm at tree line elevations. Snowpack tests suggest the snow above is currently bonding well to it. Snowpack depth decreases rapidly below tree line. Look out for early season hazards such as rocks, stumps, and open creeks.
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.
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.