Regions
Northwest Inland.
Storm slabs continue to develop at higher elevations and will be reactive to human-triggering on Wednesday. Conservative terrain choices remain critical.Use extra caution on steep south facing slopes in the afternoon if the sun is out in full force.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Wednesday is expected to be dry and mainly cloudy with sunny breaks. Alpine winds are expected to be light to moderate from the southeast and freezing levels are forecast to be 800-1100m. The next storm pulse is expected to arrive Wednesday evening. 5-10cm is expected by Thursday afternoon. Freezing levels are expected to be around 700m on Thursday with light to moderate southwest winds. Light snowfall is expected to continue on Friday.
Avalanche Summary
On Monday, isolated wind slab avalanches up to size 1.5 were reported. On Sunday, a ski cut produced a size 1 storm slab avalanche on an east aspect at 1400m elevation. The slab was 25cm thick. A small natural cycle was reported on Sunday up to size 2 and failing in the recent storm snow, mainly in the alpine. On Saturday, a natural size 1.5 wind slab avalanche was reported on a west aspect at 2200m elevation which was 20cm thick. Wind slabs are expected to be reactive to human-triggering on Wednesday. In the far north, deeply buried persistent weak layers may still be reactive to large triggers such as a small avalanche stepping down or a cornice failure.
Snowpack Summary
Up to 60cm of snow has accumulated over the past week and overlies a melt freeze crust which extends up to around 2000m elevation. This recent snow is reported to be bonding well to the crust. Moist snow was reported below 1100m on Sunday and wet snow below 800m. Recent wind has redistributed the surface snow at higher elevations forming wind slabs in leeward features. The early January surface hoar/facet layer is down around 1m+ and remains a concern for commercial operations. This layer seems the most reactive in the north of the region but may still be a concern in the south as well. Shallow snowpack areas in the east and north of the region may have a weak base layer of facetted snow on or just above the ground.
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.