We are seeing increased avalanche activity due to a potent combination of new snow, wind, warmth, and in some areas a tricky weak layer in the upper snowpack. On Saturday in particular, dangerous avalanche conditions exist. Be conservative.
Weather Forecast
Saturday: Steady snowfall Friday night easing to flurries (total 5-15cm expected). Ridgetop winds Extreme SW, easing to Moderate. Treeline Temps: High -4, Low -7.Sunday: Light snowfall. Ridgetop winds Light. Treeline Temps: High -8, Low -11.Monday: Light snowfall tapering off. Ridgetop winds Moderate SW. Alpine Temps High -9, Low -12
Snowpack Summary
Intense wind transport on Friday is creating Wind Slabs on lee slopes, over older wind slab layers. Down 50-80cm in some areas is a Persistent Weak Layer of small facets, 5-10cm thick. Where this layer exists (most likely on Sunny aspects at Treeline), the slab sitting on this layer is touchy. Storm slabs in sheltered areas are settling.
Avalanche Summary
On Thursday at Treeline, a small (Size 1) Persistent Slab was accidentally triggered by a skier, on a steep, South facing, cross-loaded slope, and a small natural Storm Slab was observed on a SE aspect. On Friday, several natural Small - Large (Size 1.5 - Size 2) Wind Slabs were observed. These were on N and E (lee) aspects, from 1950m to 2350m.
Confidence
Due to the number of field observations
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.