Avalanche Forecast
Issued: Dec 20th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
ghelgeson,
Avalanche Canada
50 to 100 cm of recent storm snow now rests on a smorgasbord of weak layers in our upper snowpack. It's time to scale the objectives way back and enjoy the simple pleasure of riding mellow well-supported treed features that are out of the wind and free of overhead hazard.
Summary
Confidence
Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.
Weather Forecast
Looks like we’re moving into a bit of a clearing trend this week.
SUNDAY NIGHT: Freezing level lowering to valley bottom, moderate west/southwest wind, 1 to 5 cm of snow possible.
MONDAY: Broken cloud cover, freezing level at valley bottom, light variable wind, a few cm of snow possible.
TUESDAY: Broken cloud cover, freezing level near valley bottom, light northerly wind, no precipitation expected.
WEDNESDAY: Broken cloud cover, freezing level near valley bottom, light southerly wind, no new snow expected.
Avalanche Summary
Over the weekend a natural avalanche cycle took place with avalanches averaging size 1.5 to 2.5, but there were a few size 3 and even size 3.5's in the mix too.
On Friday natural slab avalanches to size 3 were reported on all aspects. Â
Snowpack Summary
An active storm cycle has produced 50 to 90 cm of storm snow over the last week which rests on a weak layer of surface hoar in many areas. This new snow has combined with south/southwest wind to form reactive slabs which are especially problematic at higher elevations.Â
A weak layer that was buried in early December is now down 50-110 cm. This layer is variable and has been reported to exist as either a crust or surface hoar. In any case, it is a persistent weak layer with a significant load above it now, and it may react easily to human triggers.
Another crust that was buried in early November can be found near the base of the snowpack. There have been no recent avalanches reported on this layer, however it may be possible to trigger it from shallow, rocky terrain.
Terrain and Travel
- Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
- Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
- Be aware of the potential for large avalanches due to the presence of a persistent slab.
Problems
Storm Slabs
50 to 100 cm of storm snow has fallen in the last week and human triggered avalanches remain likely. The storm snow rest on a variety of weak layers and the snowpack will need more time than usual to adjust to this new load.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
This storm pushed the persistent slab problem over the tipping point resulting in very large avalanches Sunday. The slab rests on a persistent weak layer which has the capacity to propagate avalanches across terrain features. Wind exposed features are expected to be particularly volatile.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 21st, 2020 4:00PM
