Safe backcountry travel requires caution and good terrain selection at this time. Avalanches have been easily triggered by light loads.
Weather Forecast
Wednesday: Dry. Freezing level around 1000 m. Ridgetop winds 30-40 km/h from the southwest. Thursday: Light flurries. Freezing level around 1500 m, although local areas, especially in the north of the region, could see higher freezing levels with pockets of warm air. Ridgetop winds around 30 km/h from the southwest. Friday: At present this region looks like it will stay mostly dry, but models are uncertain with an approaching storm that could bring some snow and/or rain to this region. Strong southwest winds and rising freezing levels likely.
Avalanche Summary
Numerous avalanches were reported to have run during and immediately after the most recent storm. While most avalanches were in the size 1.5 to 2 range and ran on mostly north as east aspects from 1300 m to 2300 m, there were some larger avalanches that initiated in alpine start zones that were reported as size 3 avalanches. In at least one case, an avalanche stepped down to the mid-December weak layer.
Snowpack Summary
Between 30 and 50cm of new snow has fallen since Friday night, and has been distributed by strong winds into deeper, more cohesive deposits in higher wind-exposed terrain. The new snow overlies widespread 10-30mm surface hoar and a sun crust on steep sun-exposed slopes. I would expect continued touchy conditions, especially in areas where the recent snowfall exists as a cohesive slab.The still problematic mid-December surface hoar/crust layer is typically down 90-130cm below the surface. The reactivity of this persistent weak layer appears to be quite variable but still has the potential for large, destructive avalanches in some areas. The layer appears to be the most reactive in the south of the region at and below treeline. In these locations the surface hoar is more likely to sit directly above a hard crust.
Problems
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.
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.