Forecast winds are set to scream on Thursday. What little snow is still available for transport will feed the thin wind slabs already scattered around the alpine.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
Wednesday night: Increasing cloud and light flurries with a trace of new snow. Strong to extreme southwest winds. Thursday: Mainly cloudy with continuing scattered flurries bringing an uncertain trace to 10 cm of new snow. Strong southwest winds. Alpine high temperatures around -5.Friday: Mainly sunny before increasing cloud and flurries begin in the evening. Strong to extreme southwest winds. Alpine high temperatures jumping to about 0 as freezing levels reach 2300 metres.Saturday: Increasingly clear as cloud and light flurries ease over the day. Strong to extreme southwest winds easing over the day. Alpine high temperatures around -5 with freezing levels back to about 1600 metres.
Avalanche Summary
No new avalanches have been reported in the region, but rugged travel conditions at lower elevations have lately been discouraging travel in the alpine, where the bulk of our current avalanche danger resides.
Snowpack Summary
About 15-20 cm of new snow has buried previous snow surfaces that ranged from soft power to hard wind slab and sun crust. Strong winds have likely been aggressively forming storm slabs and wind slabs with the new snow at higher elevations.Beneath the new snow and old surface, the snowpack has a thin, weak structure, with the bottom half of the snowpack composed of weak facets and crusts. This basal layer has not been active, but terrain features like smooth alpine bowls with variable snowpack depths are still suspect given this snowpack structure. Currently only 30-90 cm of snow can be found in alpine areas and much less at lower elevations
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.