Regions
Northwest Coastal.
Confidence
Fair - Timing of incoming weather is uncertain
Weather Forecast
Friday: Snow overnight Thursday should give way to light snow or flurries on Friday. Freezing level near valley floor. Light to moderate winds.Saturday: Heavy precipitation (very heavy near the coast) with the freezing level climbing to 1200m by afternoon. Strong to gale westerly winds. Sunday: Moderate snow, tapering off by afternoon. Moderate to strong westerly winds. Freezing level dropping by afternoon.
Avalanche Summary
A natural avalanche cycle to size 3 was observed on Wednesday. Many avalanches failed on a facet/crust layer about 80cm deep, which is likely to continue to be a problem sliding layer as the next pulse of storm precipitation rolls in. Below treeline, moist loose avalanches were releasing in response to warming or rain.
Snowpack Summary
Roaring winds from the west and south-west have created new wind slabs at all elevations. Older, buried wind slabs were formed from northerly winds. Fluctuating freezing levels have led to a melt-freeze crust below treeline. Dynamic weather will continue to affect the region through the weekend, which is likely to cause further wind slab and storm slab development. Of concern in the snowpack is a buried crust/facet layer (down about 80cm) which is getting an ever-increasing load above it. It is beginning to produce destructive avalanches in some areas as a critical balance is reached.
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.
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.