Up to a metre of storm snow has fallen since Saturday and the incoming warm front will bring rising temperatures and strong winds. The perfect recipe for a widespread avalanche cycle.
Confidence
Moderate - Forecast snowfall amounts are uncertain
Weather Forecast
A warm front of 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 5-15 cm. Ridgetop winds strong from the SW, alpine temperatures near -3 and freezing levels 1200 m.Friday: Periods of snow 5-20 cm. Ridgetop winds light gusting to 80 km/hr from the SW, alpine high of -3 and freezing levels 1300 m.Saturday: Snow 5-10 cm. Ridgetop winds generally light with strong gusts. Alpine temperatures high of -2 and freezing levels 1300 m.
Avalanche Summary
On Wednesday, the region saw widespread natural and explosive controlled avalanche activity up to size 2. These avalanches failed within the recent storm snow mostly from N-NE aspects above 1950 m. Natural Loose dry avalanches up to size 1.5 were also reported from all aspects and elevations.
Snowpack Summary
Another 36 cm overnight of low density storm snow with accumulations up to 93 cm since Saturday. Strong ridgetop winds are likely transporting the new snow onto leeward slopes, building thicker and stiffer slabs. This new snow continues to bury a plethora of old snow surfaces including surface hoar, old wind slab and a sun crust on solar aspects and it also sits above a thick rain crust below 1900 m. Isolated basal weaknesses may still exist in shallow snowpack areas. These weak areas appear to be on north-northeast aspects in the alpine.
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.