Regions
Northwest Inland.
Recently formed storm slabs and wind slabs will continue to be reactive to human-triggering on Friday and conservative terrain selection remains very important.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Unsettled conditions are expected for Friday with periods of light snowfall and sunny breaks. Alpine winds are expected to be moderate to strong from the southeast and freezing levels are forecast to reach around 1000m in the afternoon. Dry conditions with a mix of sun and cloud is expected for Saturday with moderate southerly winds in the alpine and freezing levels around 700m. A mix of sun and cloud is currently forecast for Sunday morning with a weak storm pulse arriving Sunday evening.
Avalanche Summary
On Wednesday, two size 1 wind slabs were skier triggered. Both were wind-loaded features at treeline and one was reported to be 20cm thick. On Tuesday, a size 1 storm slab was ski cut on a convex roll at treeline. Recently formed storm and wind slabs are expected to remain reactive to human-triggering on Friday. If the sun comes out, natural avalanches are possible on steep south facing terrain features. 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
40-80cm 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 1200m on Wednesday 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.