Avalanches continue to be triggered by light loads in this region. Forecast warm temperatures are likely to continue this trend.
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain on Saturday
Weather Forecast
Thursday: Flurries. Freezing levels rising to around 1300 m. Ridgetop winds 20-30 km/h from the southwest. Friday: Light snow the afternoon. Freezing levels around 1200 m, ridgetop winds rising to 40 km/h from the southwest. Saturday: moderate or possibly heavy precipitation starting in the afternoon currently looks to be in the 10-15 mm range. With freezing levels heading as high as 2500 m, this will likely fall as rain on all but the highest peaks.
Avalanche Summary
Numerous natural and human-triggered avalanches were reported to have run during and after the most recent storm, up to and including Tuesday 20th, which is the most up-to-date info at the time of writing. While most avalanches were in the size 1.5 to 2 range and ran on mostly north to east aspects from 1300 m to 2300 m, there were some larger avalanches that initiated in alpine start zones up to size 3. 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.
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.