Avalanche hazard is high. As it decreases over the next few days, conditions will remain very tricky.
Confidence
Fair - Forecast snowfall amounts are uncertain
Weather Forecast
A Pacific frontal system reaches the Interior Tuesday afternoon bringing snow amounts will anywhere from 10-25 cm. This will be accompanied by moderate west ridgetop winds, switching NW by the afternoon. Treeline freezing levels will hover around 1000 m. By Thursday an upper ridge will build behind the cold front bringing cooler conditions with mostly cloudy skies and light snow.
Avalanche Summary
On Monday, numerous natural, skier triggered and remotely triggered avalanches occurred from distances up to 40 m away. Most of these were size 1-2.5, with one avalanche reaching size 3. These avalanches have been failing on a buried surface hoar layer 30-60 cm down, and with new snow and wind in the forecast the slab above this layer will grow thicker. Best case scenario is that the new storm snow will initiate a widespread natural avalanche cycle, however; if it doesn't reach its tipping point then it will likely be primed for rider triggers.
Snowpack Summary
New snow 15-30 cm, accompanied by moderate-strong SW winds will add additional load to the upper snowpack. This brings storm snow totals 40-90 cm above a very touchy surface hoar layer that was buried mid-December. Below 2100 m this storm slab sits on a thick, solid crust that has been reacting as a perfect sliding layer. Storm slabs will blanket the region and be very touchy to the weight of a skier/ rider, especially in locations that has seen wind effect. A hard rain crust with facets from early November is buried over 1 m down and is still reactive to light loads in some locations.
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.