Watch for fresh winds slabs and avoid shallow spots and rocky terrain where triggering deeper weak layers is more likely.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
MONDAY NIGHT: Cloudy with clear breaks. Light west wind. Alpine low -12, freezing level valley bottom.TUESDAY: Cloudy with isolated flurries, trace accumulation. Moderate to strong west wind. Alpine high -10C, freezing level valley bottom.WEDNESDAY: Cloudy with scattered flurries, 5-10 cm snow. Light to moderate west wind. Alpine high -6C, freezing level 1100 m.THURSDAY: Cloudy with sun and isolated flurries, trace accumulation. Light west-northwest wind. Alpine high -6C, freezing level 1200 m.
Avalanche Summary
A size 1.5 natural wind slab avalanche was observed in steep terrain on Sunday. Skier traffic produced a few small (size 1) avalanches in the new snow on Thursday.The most recent reports of larger avalanches are from over a week ago, when warm temperatures stressed the deeper layers in the snowpack and produced a few size 2 avalanches.
Snowpack Summary
Winds have redistributed up to 20 cm recent snow into wind slabs in the alpine and treeline. This new snow buried large surface hoar crystals and/or sun crusts, which could eventually develop into a touchy problem as snow accumulates. The most suspect terrain features will be steep slopes and rolls below 2000 m (where the largest surface hoar exists) and steep south-facing slopes in the alpine (where sun crusts exist). Large variability in snow depths still exists in the region, ranging from almost no snow to nearly 200 cm in some areas. For average snowpack areas, expect to find weak and sugary faceted snow around 50 to 100 cm deep, which extend to the ground. This weak bottom half of the snowpack has been the culprit for large avalanches in the region over the past few weeks.
Problems
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.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.