A warm and windy storm is driving danger up on Friday.
Confidence
Moderate - Freezing levels are uncertain
Weather Forecast
Friday brings another 10-20 cm snow, moderate to strong SW winds and freezing levels around 1500 m. A few more cm are expected on Saturday, before a change to light winds, cool temperatures, cloudy skies and a few flurries by Sunday. For more details check out https://avalanche.ca/weather.
Avalanche Summary
Numerous size 1-2 slabs were triggered naturally and by skiers over the last few days. Many of these failed at and below treeline, on buried surface hoar, about 20-40 cm deep. Many of these were triggered remotely, highlighting the volatility of the persistent slab. An increasing number of wind slabs have also been failing at alpine/ treeline elevations, and also running on surface hoar. Forecast rain at low elevations on Friday may lead to wet loose/ wet slab activity, while higher up the mountain, continued storm slab and persistent slab activity is likely.
Snowpack Summary
New snow, rising temperatures and strong winds are likely to create storm slabs in many places and wind slabs on features lee to the south. This will also add load and stress to the already volatile persistent slab. This 30-60 cm persistent slab overlies a variety of surfaces including large surface hoar, sun crusts, and facets. The persistent slab is ripe for human and natural triggers and is especially touchy at and below treeline. The mid and lower snowpack are generally well settled and strong.
Problems
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.
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.