High avalanche danger is expected to continue for another day due to new storm slabs, high freezing levels, and above freezing air trapped in the alpine.
Confidence
Poor - Freezing levels are uncertain
Weather Forecast
Snow ending Tuesday night, with a chance of flurries on Wednesday. Warm (above freezing) air that moved into the alpine on Tuesday is forecast to persist on Wednesday. Valley bottoms are forecast to warm up and the freezing level should go up to 1500 metres. The above freezing layer should be between 2000-3000 metres. Moderate to strong Westerly winds are expected on Wednesday afternoon. Gradual clearing and cooling on Thursday with light winds and no precipitation. Mostly clear and cool with light winds on Friday.
Avalanche Summary
Widespread natural and explosives control avalanches up to size 3.0 on Monday. Natural avalanche activity may have ended by Wednesday, but I think that human triggered avalanches will be very likely.
Snowpack Summary
There has been about 60 cm of new snow in the Monashees, and about 50 cm in the Selkirks in the past 48 hours. On Tuesday warm (above freezing) air moved into the alpine and freezing levels climbed up to about 1800 metres. I suspect that the warm temperatures caused rapid settlement in the dry storm slab resulting in a higher likelihood of triggering. Rain or freezing rain have created a moist slab at treeline in the Monashees. The Selkirks may be a bit cooler and drier; alpine temperatures around Revelstoke were -2.0 on Tuesday afternoon. The new storm slab is 60-80 cm thick and is sitting on a mix of old surfaces including patchy surface hoar and old windslabs on most aspects. Deeper down (around 100 cm) the mid-December surface hoar/crust layer continues to allow for remote triggering and long fracture propagations.
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.