Regions
Northwest Inland.
Confidence
Fair - Timing, track, or intensity of incoming weather is uncertain for the entire period
Weather Forecast
A series of frontal systems will affect the area for the next few days.Thursday: Strong to gale NW winds. Alpine temp -6. Moderate snow. Friday: Moderate W winds. Alpine temp -7. Light snow.Saturday: Light winds. Alpine temp -10. Moderate to heavy snow.
Avalanche Summary
We have no reports of avalanches during Monday or Tuesday, but that may be due to a lack of observations more than a lack of avalanches. In the NW Coastal region, the basal weakness was triggered by heavy loads (cornice fall, surface avalanches stepping down and explosives) to produce very large avalanches. Strong W-NW winds triggered a natural avalanche cycle inland on Sunday, with several slabs to size 2 failing behind cross-loaded ribs and gullies. A size 2.5 slab from the headwall above the Hankin-Evelyn area is suspected to have failed on the Nov crust/facet layer.
Snowpack Summary
New and buried wind slabs exist on a variety of slopes due to strong, variable winds over the last week. In the alpine, some areas are scoured to rock, while you may find 2 m + in windloaded areas. A rain crust formed a couple of days ago on low elevation slopes. Surface hoar is buried in the upper pack at treeline in isolated sheltered areas. We haven’t had any recent reports of reactivity on this layer. A November crust/facet layer near the base of the snowpack has the potential for deep releases, particularly from a thin-spot trigger point or with a heavy trigger like cornice fall or a surface avalanche stepping down. Expect new storm slabs and wind slabs to develop during the remainder of the week as a series of fronts hits the region.
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.