Strong to extreme winds and new snow are driving the danger ratings. Slab avalanches are primed for rider triggering.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
An organized low pressure system will track across the region bringing rising freezing levels, more snow and strong winds. Conditions will remain unsettled through the forecast period. Enhanced snow amounts may be greater than forecast for Saturday/ Sunday.Thursday: Cloudy with snow 5-10 cm. Ridgetop winds strong from the SW, alpine temperatures near -7 and freezing levels 1300 m.Friday: Periods of snow 5-15 cm. Ridgetop winds light gusting to 80 km/hr from the SW, alpine high of -5 and freezing levels 1400 m.Saturday: Snow 5-10 cm. Ridgetop winds generally light with strong gusts. Alpine temperatures high of -5 and freezing levels 1400 m.
Avalanche Summary
Several explosive triggered slab avalanches up to size 2.5 were reported on Wednesday.
Snowpack Summary
Another 20 cm of low density storm snow arrived overnight bringing the recent snow totals up to 50 cm since Saturday. Strong southwesterly winds will likely transport the new snow onto leeward slopes, building thicker and stiffer slabs. The new snow may have a poor bond to previous old snow surfaces that primarily consist of stiff wind slabs, crusts and facets. 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.