Another winter storm will likely build fresh and reactive storm slabs by Wednesday afternoon and into Thursday, especially on leeward slopes that see more wind loaded snow.
A layer of weak facets (sugary snow) can be found down 40-70 cm over a crust that formed in early December. This layer has produced large avalanches from explosive triggers and has shown reactivity in snowpack tests. Avoid likely trigger spots such as steep, convex slopes, with a shallow or thick to thin snowpack.
Reactive storm slabs will likely build through the day with new storm snow and strong southwest wind.
In exposed areas, strong to extreme winds have stripped many areas back down to the early December curst and create deposits of hard wind slab in lees. This wind loading may be lower down on slopes than you may expect as a result of the high wind values.
Enhanced snowfall amounts are possible on Wednesday through Thursday as a warm and wet air mass rises from the South and collides with the predominant colder air mass which is sliding down from the North.
Tuesday Night: A trace of new snow accompanied by strong ridgetop wind from the SW. Alpine temperatures near -10 and freezing levels at the valley bottom.
Wednesday: New snow throughout the day, 10-20 cm of accumulation. Strong to extreme ridgetop wind and alpine temperatures near -8. Freezing levels valley bottom.
Thursday: Heavy snowfall amounts, possibly up to 30 cm accompanied by strong SW winds. Alpine temperatures near -5 and freezing levels rising 1000-1500 m.
Friday: Mostly cloudy with some flurries. Gusty ridgetop winds from the South and freezing levels dropping back to the valley bottom.
On Tuesday, several wind slabs up to size 1.5 were reported.
On Monday, operators reported one size 2.5 persistent slab avalanche triggered with explosives on a southeast aspect at treeline. They also ski cut isolated pockets of wind slab up to size 1.
With new snow and strong wind, fresh and reactive storm and wind slabs will be likley through the forecat period.
New snow and wind will likely build reactive storm slabs through Friday. In exposed areas, strong to extreme winds will strip many areas back down to the early December curst and create deposits of hard wind slab in lees. This wind loading may be lower down on slopes than you may expect as a result of the high wind values.
Below this new snow, a layer of more consolidated snow sits over a substantial crust that formed in early December. This crust is up to 20 cm thick and is present across all aspects below 2400 m. Up to 10 cm of faceting has been reported above this crust. This problem is particularly hard to predict and tricky to manage. For this reason, wide conservative terrain margins and disciplined backcountry travel techniques will be very important. Get more details and photos in our forecaster blog.
Snowpack depths vary due to strong to extreme southwest winds that stripped snow off of exposed areas and deposited it onto lee slopes. Below 2300m, several early season crusts make up the lower snowpack. Snowpack depths range from 80-150 cm at treeline elevations and taper quickly below 1900m.
