Avalanche Forecast
Issued: Dec 13th, 2022 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs and Storm Slabs.
lbaker,
Avalanche Canada
We continue to receive reports of large natural and human-triggered avalanches on the persistent weak layer. Keep your terrain choices conservative and be prepared to back off quickly if you find signs of instability; whumpfing and shooting cracks.
Read our featured blog to learn more about how to manage a persistent slab problem when traveling in the backcountry.
Summary
Confidence
Moderate
Avalanche Summary
On Monday, a pair of size 2 human-triggered avalanches were reported in the RMR backcountry. These included a skier accidental and a skier remote from 50 m away on the mid-November layer.
Evidence of several natural storm slab avalanches was observed to have released on the Dec 5 weak layer. A few natural persistent slab avalanches, size 2.5, were reported to have released or 'stepped down' from smaller avalanches onto deeper instabilities.
Explosive control triggered several persistent slab avalanches up to size 3 in the eastern part of the region.
Snowpack Summary
Small surface hoar is forming on 40 - 50 cm of settling storm snow. On south-facing slopes snow sits on a sun crust and in sheltered terrain it overlies a weak layer of 5mm surface hoar. In the alpine northerly winds are redistributing available snow into deep pockets in lees.
Buried 60 to 90cm deep, a persistent layer of surface hoar, crust, and faceted crystals is the primary concern within the snowpack. This layer has been most reactive at treeline between 1700-2200 m, but it was also observed as low as 1450 m and on all aspects.
Snowpack depths are highly variable and range from 90cm at treeline to 200cm in the alpine in wind-affected locations.
Weather Summary
Tuesday Night
Mainly cloudy, isolated flurries trace accumulation. Northerly ridge wind 20 - 40 km/hr. Alpine temperatures, low of -10. Freezing levels valley bottom.
Wednesday
Sunny with cloudy periods. Northerly ridge wind 30 - 50 km/hr. Alpine temperatures, high of -8. Freezing levels valley bottom.
Thursday
Partly cloudy skies. Northwesterly ridge winds 40 - 60 km/hr. Alpine temperatures, high of -8. Freezing levels valley bottom.
Friday
Partly cloudy skies. Northwesterly ridge winds 40 - 60 km/hr. Alpine temperatures, high of -8. Freezing levels valley bottom.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Be aware of the potential for large, destructive avalanches due to the presence of deeply buried weak layers.
- Give the new snow several days to settle and stabilize before pushing into bigger terrain.
- Avoid open slopes and convex rolls below treeline where weak layers may be preserved.
- Be carefull around freshly wind loaded features.
Problems
Persistent Slabs
A weak layer of surface hoar and facets from mid-November is buried 50 to 90cm deep. This layer continues to be reactive to natural and human triggers, producing large avalanches and catching professionals off guard. Use extra caution at treeline where this layer is more prominent and look for signs of instability like shooting cracks, whumpfing and recent avalanches.
Aspects: All aspects.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
Storm Slabs
30 - 50 cm of snow has settled into a soft slab above a weak layer of 5mm surface hoar. Be aware that as winds begin to blow from the north, the slab will become more cohesive and additional load will be to added on to this weak layer. This may result in another avalanche cycle on this layer in exposed areas.
Don't forget that if triggered surface slabs could step down to deeper layers resulting in larger and more destructive avalanches.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 14th, 2022 4:00PM
