New snow, wind, and warm temperatures will drive the avalanche hazard over the weekend.
Confidence
Fair - Due to the number of field observations
Weather Forecast
Saturday: Cloudy with flurries expected to bring no more around 5cm of new snow. Freezing levels expected to remain at or near valley bottoms with treeline temperatures around -2. Ridge top winds are expected to be moderate westerlies. Sunday: Moderate snowfall with 10-15cm of accumulation, freezing levels rising up to 1800m and strong southwesterly winds. Monday: Light snowfall with less than 5cm of accumulation, freezing levels around 1500m and strong westerly winds.
Avalanche Summary
Reports from yesterday are limited to a few loose sluffs from steep terrain. On Tuesday, a wind slab avalanche size 1.5 was easily triggered under the weight of a rider from a NE aspects.
Snowpack Summary
Light incremental snowfall is starting to bury surface hoar and a faceted upper snowpack. Snowpack depths at treeline seem to vary from 70 - 110 cm with high variability in wind-exposed areas. A persistent weakness of buried surface hoar and facets, with an associated crust, is down approximately 20-40cm . Recent reports suggest this layer has been producing variable results with snowpack tests, but it may become reactive as a cohesive slab develops with warming and/or additional load. The base of the snowpack is made up of weak facets and depth hoar. This deep persistent weakness may be stubborn to trigger, especially in deeper snowpack areas, but the sensitivity to triggers likely increases in shallower locations, especially on a steep, convex slopes.
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.
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.