Avalanche Forecast
Issued: Dec 12th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Persistent Slabs.
rbuhler,
Avalanche Canada
Wind slabs and persistent slabs remain a concern throughout the region and conservative terrain selection remains essential. The wind is expected to switch directions on Monday so wind slabs should be expected on all aspects in exposed terrain.
Summary
Confidence
Weather Forecast
An Arctic ridge of high pressure brings cold and dry conditions with outflow winds to the region for the next few days.
Sunday Overnight: Mainly cloudy with isolated flurries, light to moderate S winds, treeline temperature around -12 °C.
Monday: Mainly sunny, moderate to strong E-NE winds, treeline high around -10 °C.
Tuesday: A mix of sun and cloud, moderate variable winds, treeline high around -16 °C.
Wednesday: A mix of sun and cloud, light to moderate variable winds, treeline high around -14 °C.
Avalanche Summary
On Saturday, two natural size 2 wind slab avalanches were reported on NW aspects in the alpine and explosives were triggering storm slab avalanches up to size 3. On Friday, a natural avalanche cycle was reported with storm slabs up to size 3. These slabs were typically around 40 cm thick but some were reported as thick as 100 cm.
On Monday, wind slabs are expected to be very reactive to human triggering and natural wind slab releases are possible. Older wind slabs are most likely found on north and east aspects but as the wind switches direction on Monday, new wind slabs are expected to form on south and west aspects. The persistent slab problem remains a concern and human triggering of this layer is possible with the layer typically down 40-70 cm.
Snowpack Summary
Between Friday afternoon and Sunday morning, there has been 25 to 40 cm of new snow across the southern half of the region, and 15 to 20 cm in the North around Bear Pass. This brings the typical storm accumulations across the region to 40-70 cm since last Tuesday. Recent strong SW winds have formed reactive wind slabs in exposed terrain. On Monday, new wind slab formation is expected as the winds switch direction to an outflow pattern and as a result, reactive wind slabs may be found on all aspects.
The December 7 persistent weak layer is now down 40-70 cm and may include a crust, facets, and/or surface hoar. This layer appears to be gaining strength but may still be reactive to human triggers in some areas. A bit deeper in the snowpack is the December 1 crust/facet layer which generally appears to have stabilized but may still be reactive in isolated areas.
Terrain and Travel
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Be aware of the potential for large avalanches due to the presence of buried weak layers.
- Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
Problems
Wind Slabs
Reactive wind slabs formed over the weekend primarily on north and east aspects as a result of strong SW winds. On Monday, the wind is expected to switch directions and new wind slab formation is expected primarily on south and west aspects. As a result, reactive wind slabs should be expected on all aspects in wind exposed terrain.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
There is still concern for persistent weak layers like facets and surface hoar which may rest on the crust which was buried last week and is now typically down 40 to 70 cm below the surface. This interface appears to be gaining strength in many areas but remains a concern for professionals in the region. Triggering an avalanche on this layer would result in a large, destructive avalanche so extra caution remains critical.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 13th, 2021 4:00PM
