The storm is forecast to continue overnight. New snow, wind, and warming temperatures are keeping the avalanche danger HIGH.
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
The next pulse of Pacific moisture is forecast to move into the region on Monday afternoon and intensify overnight. Expect 15-20 cm of snow by Tuesday morning combined with strong Westerly winds and another 10-15 cm during the day as the winds decrease to moderate values. The storm snow should end by Wednesday morning, but strong winds and rapidly rising freezing levels (up to about 1300 metres) are expected to continue during the day on Wednesday. A ridge of High pressure is forecast to build over the region on Thursday bringing drier conditions, clearing skies and cooling temperatures.
Avalanche Summary
No new avalanches reported. I suspect that new storm snow avalanches either released naturally today or were easy to trigger.
Snowpack Summary
10-20 cm of dry new snow has combined with the 30-50 cm of recent snow to develop a storm slab above a mix of old surfaces including wind slabs on several aspects. The stiffness of the new storm slab has been reported to be variable across the region. Previous warm air in the north has likely made the snow dense in some places, while colder air in the East has resulted in less consolidated snow. The persistent mid-December crust/surface hoar layer appears prominent in the south of the region and is still reported to fail easily during snowpack tests. It is most prominent at within a few hundred metres of treeline elevation. On average it can be found around 80 cm below the surface, although it has variably been reported anywhere from 30-90 cm below the surface. In the north of the region, this layer is present, although reported to be harder to trigger. Further down, a hard rain crust with facets from early November is buried more than a metre down and is currently unreactive. However, triggering from shallow rocky and unsupported terrain remains a concern.
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.