Forecast heavy snow and wind will result in high avalanche danger.
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Snow above 1000 metres combined with moderate southwest winds tonight and Monday morning. 15-30 cm of snow is forecast for alpine elevations by late Monday morning. Monday should be cloudy with some lingering flurries and light easterly winds. Freezing levels should drop down to valley bottoms by Tuesday morning. Mostly sunny with light winds on Tuesday and freezing levels rising up to about 2000 metres. Cloudy on Wednesday with moderate southwest winds and light precipitation.
Avalanche Summary
No new avalanches reported. I expect that forecast new snow and wind will develop new storm slabs in the alpine and at treeline on all aspects.
Snowpack Summary
Up to 40 mm of rain fell on Saturday that may have been snow above 2000 metres. Gradual cooling and forecast heavy precipitation for Sunday night and Monday are expected to develop new storm slabs above various old surfaces including moist or wet snow, crusts, old windslabs, and possibly surface facets on high alpine north aspects. There is not enough snow at below treeline elevations for avalanches at this time. If the freezing levels drop to valley bottom we may see new snow covering some areas that have been bare ground. The most prominent snowpack feature is a thick crust 10-30cm below the surface (before the ongoing storm), extending up to around 2200m elevation. The support of this crust is breaking down in response to warm temperatures. Persistent weak layers below this crust still react in snowpack tests and could wake up with continued warming or loading.
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.