Avalanche Forecast
Issued: Dec 17th, 2019 3:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
cgarritty,
Avalanche Canada
Continuing snowfall will build up storm slabs while bringing increasing stress to an active and deeply buried weak layer at higher elevations. Expect stability to deteriorate over the day.
Summary
Confidence
Moderate - Forecast snowfall amounts are uncertain.
Weather Forecast
TUESDAY NIGHT: Cloudy with continuing flurries bringing 10-15 cm of new snow. Strong southwest winds.
WEDNESDAY: Cloudy with continuing flurries bringing another 10-15 cm of new snow, continuing overnight. New snow totals of 20-30 cm by end of day. Moderate to strong south wind. Alpine high temperatures near -4 with freezing level to 1000 metres.
THURSDAY: Cloudy with continuing flurries bringing approximately 10-20 cm of new snow and 3-day snow totals of up to 50cm. Snowfall increasing overnight. Light to moderate south winds. Alpine high temperatures around -4 with freezing levels near 1000 metres.
FRIDAY: Cloudy with easing flurries and 20-30 cm of snow from the overnight period. Light southwest winds. Alpine high temperatures around -5.
Avalanche Summary
We haven't yet received reports of avalanches from Monday and Tuesday's new snow, but there were a few persistent slab avalanches reported on Saturday, both natural and human triggered, up to size 2.5. Click here to check out a MIN report of a persistent slab avalanche in the Whistler backcountry on Saturday.
On Friday, there were several reports of natural, human and explosives triggered avalanches up to size 2. The majority of these avalanches released on the persistent weak layer that was buried in mid November.
On Thursday, there were several reports of human and explosives triggered avalanches up to size 2. Some of these avalanches stepped down to the mid November weak layer.
Looking forward, activity of this nature can be expected to continue and perhaps intensify as snowfall increases stress on buried weak layers.
Snowpack Summary
New snow from a series of storms has begun to bury a new weak layer of surface hoar at lower elevations as well as a glaze of rime crust above 1900m. The new snow adds to 15-25 cm of recent snow sitting on another layer of surface hoar in sheltered areas, as well as sugary, faceted snow elsewhere.
Perhaps most importantly, continuing snowfall will increasingly stress a persistent weak layer from mid November that consists of a crust/facet combination, recently found approximately 35-70 cm deep. This layer has been responsible for several recent avalanches. Snowpack tests consistently indicate that slabs overlying it can be triggered by humans and propagate widely, resulting in large avalanches.Â
The snowpack is unusually shallow and weak for the Sea to Sky region. Persistent weak layers like the above mentioned mid-November crust/facet combination can occur in any season, but they are not the norm here. They demand especially thoughtful and conservative terrain selection.
Total snowpack depths range between 80-200 cm and taper quickly at lower elevations.
Problems
Storm Slabs
New snow is accumulating above a new array of weak surfaces. Expect new accumulations to trigger increasingly easily as the depth and cohesion of new snow increases. For this reason wind loaded areas should be especially concerning. Lower elevations may be affected in areas where new snow falls on smooth surfaces
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
A persistent weak layer has been responsible for numerous recent avalanches. This scenario is atypical for the Sea to Sky region, and needs to be treated with serious caution. The likelihood of triggering a large persistent slab avalanche will be increasing as new snow accumulates.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 18th, 2019 5:00PM
