Regions
Northwest Coastal.
Storm slabs may continue to be reactive due to the forecast new snow and wind overnight. Avalanche danger will trend down with forecast cooling in the next few days.
Confidence
Moderate - Forecast snowfall amounts are uncertain on Sunday
Weather Forecast
Overnight: 5-10 cm of new snow with freezing levels down to 400 metres, and moderate west winds. Sunday: Cloudy and unsettled with a chance of convective flurries. Daytime freezing level up to 800 metres. Monday: Overnight freeze down to 500 metres followed by mostly sunny skies and light winds. Tuesday: Overcast with light snow and increasing southerly winds.
Avalanche Summary
On Friday we had one report of a loose wet avalanche size 1.0 that released from a ski cut below treeline in the Shames area. One natural ice fall and one natural cornice fall size 3.0 were reported from the Bear Pass area on Thursday. Numerous natural storm slabs up to size 2.0 were reported on Wednesday. I suspect that storm slabs were active on Saturday due to the combination of new snow, warm temperatures, and moderate to strong winds.
Snowpack Summary
Storm slabs continue to develop in the alpine and at treeline. Warm daytime temperatures have created moist snow at treeline and wet snow below treeline. In the Shames area on Friday there was 12 cm of moist storm snow above the most recent melt-freeze crust. The top 40-60 cm of the snowpack at 1200 metres was reported to be moist, and the late February layer was down 118 cm producing moderate sudden collapse shears. The late February persistent weak layer continues to be a concern for triggering large avalanches. This combination of crust and weak facets is now down 100-150 cm, and may be triggered by light additional loads in shallow weak spots adjacent to large terrain features. The snow below treeline may become weak and release as loose wet avalanches or wet slabs in steep unsupported terrain features.
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.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.