Regions
Northwest Coastal.
Confidence
Fair - Timing of incoming weather is uncertain on Saturday
Weather Forecast
Saturday: Very heavy precipitation, starting early morning as a warm front arrives. Mild temperatures. Freezing level rising through the day to around 1200m. Strong to gale southerly winds at ridge top. Sunday: Moderate snow continues. Freezing level staying near 1200m. Strong westerly winds.Monday: A break from heavy snow, although a weak disturbance may bring light snow in the afternoon. Freezing level falling back to valley floor.
Avalanche Summary
A natural avalanche cycle to size 3 (most at size 2) occurred on Wednesday and Thursday. Skiers triggered numerous size 1 slabs on Thursday, failing on an instability in the storm snow.
Snowpack Summary
Heavy new snow has arrived this week and looks set to continue through the weekend. Roaring winds from the north-west, west and south-west have created new wind slabs at all elevations. Older, buried wind slabs were formed from northerly winds and are of particular concern at treeline and below. 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 facet layer (down about 80-120cm) 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. Below treeline, a crust /facet combo buried in early January is producing easy, sudden collapse results in compression tests.
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.