Regions
Northwest Coastal.
Confidence
Fair - Timing, track, or intensity of incoming weather is uncertain for the entire period
Weather Forecast
Monday night: Expect winds of up to 100 km/h from the SW and about 20 cm of snow overnight. Alpine temp -5.Tuesday: Westerly winds dropping to moderate. Alpine temp -6. Light snow. Freezing level 800 m, dropping to surface overnight.Wed: Light westerly winds. Alpine temp -7. Freezing level 100 m. Light snow.Thurs: Moderate SW winds. Alpine temp -3. Freezing level 800 m. 5 cm snow.
Avalanche Summary
On Sunday, natural activity to size 2.5 occurred in response to very strong winds, new snow and warming. This cycle is expected to continue through Monday and Tuesday.
Snowpack Summary
Storm snow is being redistributed by very strong winds, creating wind slabs on a variety of slopes. In sheltered areas below treeline, loose sluff may be encountered. New wind slabs may be sitting above widespread surface hoar, making a touchy combination. The surface hoar was particularly noticeable in the Shames backcountry on Saturday. In general the mid-pack is gaining strength. A November facet/crust layer can be found near the base of the snowpack. Observations of this layer are limited, however recent explosives testing suggests it may be more problematic in the north of the region than in the south. Above about 1000 m, the snowpack is 150-200 cm deep. Below 1000 m, the snowpack is only just reaching threshold.
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.