Safe backcountry travel requires caution and good terrain selection at this time.
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain on Saturday
Weather Forecast
Thursday: Light flurries. Freezing levels rising to around 1400 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: light to moderate precipitation starting in the afternoon currently looks to be around 5 mm. With freezing levels heading as high as 2200 m, this will likely fall as rain well into alpine areas.
Avalanche Summary
Avalanches up to size 2 were reported to have run during and immediately after the most recent storm on all aspects and at elevations from 1800-2300 m. Most avalanches were running on the most recent layer of surface hoar, with typical crown depths of 30-60 cm. There was one report of an avalanche on the more deeply buried mid-December weak layer, although it appears as though it may have been triggered in a shallow spot, as the crown depth was reported to be only 30-45 cm.
Snowpack Summary
Between 15cm and 40cm of recent snowfall has buried widespread 10-20mm surface hoar and a sun crust on steep sun exposed slopes. Strong winds have blown these accumulations into deeper deposits in higher elevation terrain. Due to the underlying surface hoar, I would expect continued touchy conditions, especially in areas where the recent snowfall exists as a cohesive slab.The mid-December surface hoar/crust layer is typically down 60-120cm 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 at and below treeline. The mid-Nov weak layer is near the bottom of the snowpack but has generally become inactive.
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.