New snowfall amounts are uncertain for Sunday. If more than 20 cm of new snow falls in your area, the local avalanche danger may be HIGH.
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain on Sunday
Weather Forecast
Two weather systems will collide today creating storm conditions over the interior regions. A cold arctic front will interact with moist air from the pacific creating heavy snowfall and moderate to strong winds.Sunday: Heavy snowfall, moderate to strong alpine winds from the SW, freezing levels around 500mMonday: Light snowfall, moderate to strong alpine winds from the NE, temperatures becoming unseasonably coldTuesday: Dry, cold, mostly sunny, moderate alpine winds from the NE
Avalanche Summary
No recent avalanches have been reported but incoming field data is still very limited.
Snowpack Summary
Highly variable snowpack conditions are being reported but typically 1m of old, well-settled snow lies below the new storm snow. New storm slabs are forming on over a variety of old snow surfaces including (1) winds slabs and wind scoured areas in the alpine and exposed areas at treeline, (2) sun crusts on steep south facing slopes, and (3) surface hoar in sheltered areas around treeline elevation and below. There are still two layers of concern within the mid/lower snowpack: the early November surface hoar is down roughly half way (50-60cm) and the October rain crust is near the ground. While these layers have recently become dormant, the weight of the new storm snow may cause these layers to reactivate in isolated areas causing large, destructive avalanches. The October crust can be found in the alpine on north aspects (likely east and west as well). The early November surface hoar appears to be spotty and drainage specific.
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.
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.