Sustained and shifting winds are expected to quickly redistribute Thursday night's snowfall into touchy new wind slabs. Seek out sheltered lower elevations on Friday.
Confidence
Moderate - Forecast snowfall amounts are uncertain
Weather Forecast
Thursday night: Flurries bringing 7-10 cm of new snow. Strong southeast winds shifting to southwest.Friday: Cloudy with continuing isolated flurries and a trace to 4 cm of new snow. Moderate to strong southwest winds. Freezing level to 1000 metres with alpine high temperatures of -10.Saturday: Mainly cloudy. Light to moderate southwest winds. Freezing level to 1000 metres with alpine high temperatures around -10.Sunday: Mainly cloudy. LIght to moderate southwest winds. Freezing level to 1000 metres with alpine high temperatures around -10.
Avalanche Summary
Reports from early in the week included several small (size 1) skier-triggered and ski cut storm slabs on high elevation north aspects. These slabs failed on a surface hoar layer buried earlier this month that is mentioned in our snowpack discussion, found down about 25 cm. Looking forward, avalanche danger will be increasing as strong southeast (then southwest) winds and light snowfall form new slabs over Thursday night. These newly formed slabs are likely to be touchy and reactive to human triggering over the near term.
Snowpack Summary
Recent light snowfalls have been followed by warm daytime temperatures and glimpses of sun, setting up a couple of thin storm snow layers over temperature and sun crusts at lower elevations and on south aspects. On shaded aspects at higher elevations, these snowfalls have buried and preserved a couple of surface hoar layers now found up to 25 cm deep. The deepest of these surface hoar layers has been the failure plane in several recent slab avalanches.New snow amounts taper with elevation and below 1800 m, minimal accumulations have buried a supportive crust on all aspects. This crust will likely break down with daytime warming, becoming moist in the afternoon. Persistent weak layers from early January and mid-December are still being reported by local operators. They are generally considered dormant, but could wake up with a surface avalanche stepping down, a large cornice fall, or a human trigger in a shallow or variable-depth snowpack area. These layers consist of sun crust, surface hoar and/or facets.
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.