A widespread crust has been buried by wind slabs at higher elevations and consolidated recent snow in sheltered areas.
A deep persistent slab problem may not seem evident or reactive but can produce very large and destructive avalanches.
Choose terrain carefully as you travel.
Last week's snowfall was accompanied by strong southwesterly winds, creating deep deposits of wind slab in lee terrain features. Wind slabs may remain reactive to human triggering for longer than is typical as they overlie a slick rain crust formed early last week.
Keep in mind that if triggered, wind slabs may step down to deeper layers resulting in very large avalanches.
A crust with weak, faceted snow above and below exists near the base of the snowpack. Human-triggering this layer is unlikely, but large loads such as cornice fall or a smaller avalanche stepping down to this layer are possible. Avoid thin, rocky, wind-affected areas where triggering this layer is most likely.
On Sunday, wind slab avalanche activity was reported to have occurred naturally and accidentally by skiers. These were size 1 to 2.
On Friday and Saturday, numerous natural and human-triggered storm and wind slabs were reported up to size 2. These slabs mainly occurred in wind-loaded terrain and primarily failed on the underlying rain crust.
Several large (size 2 to 2.5) deep persistent slab avalanches were produced during explosive control work last Thursday. All in alpine terrain on a variety of aspects with crowns of 1.5 to 2 m deep. This layer now presents a low-probability but high-consequence problem that is atypical for our coastal snowpack. Learn more about the nature of this deep persistent slab problem from this forecaster blog.
Looking forward, wind slabs may remain reactive to human triggering for longer than is typical due to the slick crust they are sitting on. Avoid wind-loaded terrain and watch for signs of instability as you travel.
Strong southwest winds, creating hard wind-affected surfaces in open areas and wind slabs in lee terrain features from the 30 to 60 cm that accumulated by the end of last week. New wind slabs and recent snow have covered a rain crust that formed on December 26th. This crust is thin and breakable at higher elevations and up 10 cm thick at lower elevations.
The mid-snowpack consists of moist snow below the crust at lower elevations. At higher elevations, a series of crusts and denser snow can be found below this December 26th rain crust.
Near the base of the snowpack, a weak facet/crust layer can be found.
Total snow depths are roughly 100 to 200 cm at treeline.
Monday Night
Cloudy with clear periods, no accumulation, winds south 15 to 30 km/h, temperatures -5 to 0 °C at 1500 m.
Tuesday
Mostly cloudy, up to 6 cm accumulation, winds south to southeast 20 km/h, temperatures -8 to -5 °C at 1500 m.
Wednesday
A mix of sun and cloud, trace accumulation, winds southeast to east 20 km/h, temperatures -5 °C at 1500 m.
Thursday
Cloudy, up to 10 cm accumulation, winds southeast 20 km/h, freezing level reaching 1600 m.
More details can be found in the Mountain Weather Forecast.
