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 15-25 cm of snow by Tuesday morning combined with strong Westerly winds and another 10-20 cm during the day as the winds decrease to moderate values and the freezing levels rise up to about 1800 metres. There is a chance of some above freezing air becoming trapped in the alpine on Tuesday afternoon and evening. The storm snow should end by Wednesday morning, but strong Westerly winds and high freezing levels (up to about 1600 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. The western parts of the region (Monashees) should get more snow on Tuesday than the Selkirks, but they will also get more warming and a chance of freezing rain.
Avalanche Summary
Natural and explosive controlled storm slab avalanches up to size 3.0 were reported from along the highway corridor. Some storm slab avalanches may have stepped down to the mid-December persistent weak layer of surface hoar and crust. Forecast new snow and wind are expected to continue to add to the very touchy new storm slab. The next pulse of warm moist air may consolidate loose snow into a more uniform slab resulting in longer fracture propagations by Tuesday.
Snowpack Summary
There has been about 40 cm of new snow in the Monashees, and about 20 cm in the Selkirks overnight. The new snow combined with moderate to strong Southwest winds developed a new storm slab in the Monashees. Reports from the Selkirks describe less snow that is colder and drier with less wind effect. The new snow and recent snow have combined into a storm slab that is about 60 cm deep. This storm slab 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. Forecast continued loading on top of the new storm slab may result in natural avalanche activity on the deeply buried weak layer.
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.