Avalanche Forecast
Issued: Dec 17th, 2021 1:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
JSmith,
Avalanche Canada
Touchy storm slabs will form throughout the day on Saturday and be most reactive in wind affected terrain. Expect the danger to be HIGH in localized areas that receive greater than 25 cm of snow.
A concerning persistent slab problem exists in much of this region. Learn more HERE
Summary
Confidence
Moderate - Uncertainty is due to the timing, track, & intensity of the incoming weather system. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.
Weather Forecast
FRIDAY NIGHT: Snow; 3-5 cm / Moderate, southwest wind / Low of -19
SATURDAY: Snow; 15-20 cm + 5-15 cm Saturday night / Strong, southwest wind / High of -12
SUNDAY: Clearing skies with flurries; 0-3 cm / Light, north wind / High of -15
MONDAY: Sunny ; Light, southwest wind / High of -17
Avalanche Summary
New snow and wind on Saturday will form touchy storm slabs reactive to human triggers.
A skier triggered size 2.5 persistent slab was reported on Tuesday. This avalanche failed on the crust layer down 40-150 cm. The photo of this avalanche in our recent blog demonstrates the layer's ability to propagate large distances, resulting in large and destructive avalanches.
Snowpack Summary
30-50 cm of recent low density snow has been redistributed by strong northwest winds which are switching to southwest with the incoming storm.Â
Forecast snow and wind on Saturday are expected to form touchy storm slabs reactive to human triggers at all elevations, but will be most reactive in wind affected terrain.
Below the new snow, the prominent layer of concern in most of the region is a crust that was formed in early December and is now down 40-150 cm, which is prime depth for human triggering.
This layer has created a persistent slab problem that has recently surprised riders with large avalanches.
Another crust layer near the bottom of the snowpack has not produced any recent avalanches but may be possible to trigger by hitting a shallow spot in the snowpack on a large alpine feature.
Terrain and Travel
- Storm slab size and sensitivity to triggering will likely increase through the day.
- As the storm slab problem gets trickier, the easy solution is to choose more conservative terrain.
- Storm slabs in motion may step down to deeper layers resulting in large avalanches.
- Be aware of the potential for large avalanches due to the presence of a persistent slab.
- Avoid shallow snowpack areas, rock outcroppings and steep convex terrain where triggering is most likely.
Problems
Storm Slabs
New snow and wind on Saturday will form touchy storm slabs at all elevations, but will be especially reactive in wind affected terrain.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
A layer of weak facets (sugary snow) can be found down 40-150 cm near a crust layer that formed in early December. This persistent slab problem has recently been most reactive at treeline elevations and is possible to human trigger on some slopes. Avoid likely trigger spots such as steep, convex slopes, with a shallow or thin to thick snowpack.
Aspects: All aspects.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
Valid until: Dec 18th, 2021 1:00PM
