40cm of new storm snow combined with strong SW winds and warm temps create perfect conditions to make slabs and cause poor stability. Large avalanches involving the entire winter snowpack are occurring. Terrain recognition and avoidance are key!
Confidence
Fair - Due to the number of field observations on Saturday
Weather Forecast
An unstable air mass over us will continue to dominate the weather over the next few days. On Sunday, winds and temps will decrease a little but we should still expect to see moderate SW winds throughout the day at treeline and above. Forecasts are calling for an additional 8-10cm overnight, then dribs and drabs throughout the day on Sunday. On Monday another pulse is expected to cross the region giving us another 10-15cm but the confidence in this system and the precip amounts are uncertain.
Avalanche Summary
Visibility was obscured throughout most of the day on Saturday and as a result, avalanche observations were limited. Forecasting staff were able to ski cut two sz 1.5 slabs within the storm snow on a steep N aspect at treeline. These slabs did not step down to the weak basal layers but this was in previously skied terrain.
Snowpack Summary
Up to 40cm recent storm snow has fallen over a variety of different snow surfaces. This snow fell under mild temperatures (-4C) and strong to extreme winds at all elevations. As a result, new storm slabs have been quick to develop and have been rapidly overloading the weak basal facets that exist throughout the region. Cracking along ridgelines and below ridgecrests was observed which is a good indicator of poor stability within the snowpack. Warm temps will allow these new avalanche problems to settle out quickly but for the time being, we are in a period of poor stability.
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.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
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.