Avalanche Forecast
Issued: Dec 11th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Deep Persistent Slabs.
kklassen,
Avalanche Canada
Even though danger ratings are moderate there's still potential problems. Avoid windloaded terrain and stay away from areas with a shallow or variable depth snowpack. Please post to the Mountain Information Network if you are in the mountains.
Summary
Confidence
Low - Uncertainty is due to the limited number of field observations.
Weather Forecast
Dig out your cold weather clothes--looks like an arctic deep freeze is on its way.
Saturday night: Cloudy with flurries, temperature dropping to -22 overnight. Wind Northeast 30kphÂ
Sunday: Cloudy with flurries, -25, wind northeast 15-30kphÂ
Sunday night: Cloudy with a few flurries, -31, wind NE 30-50
Monday: Arctic ridge building. Probably some lingering cloud, temperature -25 to -30, northeast outflow winds expected to continue.Â
Avalanche Summary
Explosive control earlier in the month produced many large avalanches that failed on the weak sugary crystals at the bottom of the snowpack. These avalanches ran full path.
On December 1, a size 2.5 avalanche was remotely triggered by a recreational group on Log Cabin. This avalanche likely failed on the weak, sugary snow at the bottom of the snowpack.Â
Natural avalanche activity and human triggered avalanches will be most likely in wind-loaded features anywhere recent winds have redistributed the snow. Triggering the deep layer (see the December 1 avalanche described above) is most likely to occur in shallow areas or where the snowpack variable in depth with a mix of shallow and deep zones.Â
Snowpack Summary
Low density snow from the last storm is being redistributed by winds that were at first southerly then switched to north and northeasterly. Old windslabs on northerly aspects are likely becoming somewhat less sensitive but expect new, potentially somewhat more sensitive windslabs on south and southwest aspects. Snow quality will be best in sheltered areas, which is also where you are least likely to find windslab problems.Â
The middle snowpack is supportive to travel but snow depth still varies greatly with aspect and elevation.Â
A layer of weak, sugary snow at the base of the snowpack has been observed in most areas. This layer was reactive earlier in December and it might still be possible to trigger this deeply buried layer in shallow snowpack areas or if a cornice fall or surface avalanche impacts a slope. If triggered, this basal layer could produce large avalanches. This sugary layer will likely become weaker in the coming days with increasingly cold temperatures potentially making it increasingly sensitive to triggering.
Terrain and Travel
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Be alert to conditions that change with elevation and wind exposure.
- Approach lee and cross-loaded slopes with caution.
- Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
- Be aware of the potential for large avalanches due to the presence of a deep persistent slab.
Problems
Wind Slabs
There's little direct information today but there was some new snow available for wind transport yesterday and southerly winds strong enough to move it were reported, notably around Paddy Peak and Powder Valley. Overnight weather station info doesn't show much wind, but outflow (northeast) winds moving snow and creating small slabs were reported. So I'm guessing there will be a mixed bag of slightly larger older and newer but maybe smaller windslabs on most aspects and various elevations. As temperatures drop, I expect sensitivity to triggering will decrease but I'd still be pretty careful on Sunday as the transition to colder weather begins.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Deep Persistent Slabs
This layer is becoming more deeply buried and somewhat harder to trigger. But it would likely result in a large avalanche if you tickle it from the wrong spot. Most likely trigger points are areas where the snowpack is shallow or variable so avoid fat to thin transitions and stick to places where the snowpack is deep. Remote triggering is possible and a cornice fall or surface avalanche could set off a deeper slide so be aware of your overhead exposure. Decreasing temperatures will initially make it harder to trigger this problem but if the cold persists, the failure layer will become weaker and we may eventually see sensitivity creeping up again in the coming days
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 12th, 2021 4:00PM
