Confidence
Fair - Due to variable snowpack conditions
Weather Forecast
A ridge of high pressure will remain imbedded over the region for the forecast period. Winds will be mostly light and southwesterly with alpine temperatures remaining well below freezing.
Avalanche Summary
Since the recent warming, numerous large and destructive avalanches (to size 3.5) were reported in the region. Most of the avalanches were specific to south-facing alpine features. Some of these avalanches were initiated by cornice fall. Others were loose, wet avalanches that, in some cases, stepped down to basal weaknesses. On Saturday a skier was injured in an avalanche near Kimberley. Details were patchy at the time this bulletin was written. I expect that avalanche activity will decrease with forecast cooling.
Snowpack Summary
The big story has been the recent weather. Over the weekend sun exposed slopes at upper elevations became moist and cornices weakened due to solar radiation and increased alpine temperatures. With forecast cooling these slopes will gain strength and a crust will develop on most slopes that were sun-affected.On shaded aspects, lingering wind or storm slabs should have gained considerable strength, but may show sensitivity to rider triggers; especially on steeper slopes and convex rolls. Below this sits a fairly well settled mid-pack. There are, however, a few exceptions. The Jan. 13th SH/FC combo has been reactive. As well, the mid December facet/surface hoar layer is buried approx. 80 cm on the east side and 200+ cm on the west side and has been more reactive in the Purcells than any other region. There are also basal facets at the ground which will continue to remain a concern, especially in the thin snowpack parts of the region. Snowpack depths at 2000m sit near 2m deep. If you're traveling around the mountains, it's a good time to take notice of what layers are developing (surface hoar/ crusts) that may become an issue once buried.
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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.