Forecast snow, wind and rising temperatures are driving the danger rating to HIGH.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Friday: Snow amounts 10-20cm by Friday afternoon. Ridgetop winds moderate from the SW. Alpine temperatures near -4 and freezing levels rising to 1500 m by the afternoon. Saturday: Snow amounts 5-10 cm. Confidence remains low in actual snow amounts and timing. Rigetop winds gusting to 75 km/hr from the SW. Alpine temperatures near -5 and freezing levels 1300 m. Sunday: Unsettled conditions continue with snow 5-10 cm. Ridgetop winds generally light from the SW and freezing levels falling to 1000 m.
Avalanche Summary
On Thursday, a size 2.5 deep persistent slab avalanche was reported from the Elkford- North riding. It looked to be 24 hrs old and likely failed earlier in the storm. It did fail within the basal facets and scrubbed down to rocks. Widespread loose dry avalanches were also noted from steep terrain features up to size 1.5. Natural avalanche activity will likely continue with warming temperatures, forecast snow and strong winds.
Snowpack Summary
Another 17 cm of low density storm snow arrived overnight bringing the recent snow totals up to 67 cm in the past week. The new snow will likely have a poor bond to previous old snow surfaces that consist of stiff wind slabs, crusts and facets. Strong southwesterly winds is redistributing the new snow onto leeward slopes, building thicker and stiffer slabs. The mid-pack in this region is generally well settled and strong, but the bottom third of the snowpack is composed of weak facets (sugary snow crystals). Approximately 100-120 cm of settled snow sits above the weak layer of sugary, rotten facets that developed mid- December. This remains a concern and should be on your radar especially when change is happening to the snowpack.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.