Avalanche Forecast
Issued: Dec 12th, 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
Numerous persistent slab avalanches caught both professionals and recreationalist off guard over the last few days. Use extra caution at treeline where triggering a persistent slab is more likely.
Read our featured blog on understanding 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. This is just the latest in a number of persistent slab avalanche reports from the last few days.
Throughout the weekend numerous size 2 storm slab avalanches were observed on the Dec 5 surface hoar weak layer. Whumpfing and cracking were observed throughout the region.
Snowpack Summary
Moderate southwest ridgetop winds have redistributed 40 - 50 cm of storm snow into deep pockets at higher elevations. On south facing slopes this new snow has fallen on a sun crust and in sheltered terrain it sits over a layer of surface hoar.
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
Monday Night
Mainly clear skies with northerly ridge winds 25 km/hr. Alpine temperatures, low of -10. Freezing levels valley bottom.
Tuesday
Mainly clear in the morning. Scattered cloud in the afternoon with the possibility of isolated flurries in the evening, trace accumulation. Northerly ridge wind 25 - 40 km/hr. Alpine temperatures, high of -6. Freezing levels valley bottom.
Wednesday
A mix of sun and cloud. Northwesterly ridge winds 30 - 50 km/hr. Alpine temperatures, high of -7. Freezing levels valley bottom.
Thursday
Clear skies. Northwesterly ridge winds 20 - 40 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
- Give the new snow time to settle and stabilize before pushing into bigger terrain.
- Avoid open slopes and convex rolls below treeline where weak layers may be preserved.
- Be aware of the potential for large, destructive avalanches due to the presence of deeply buried weak layers.
- Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
Problems
Persistent Slabs
A weak layer of surface hoar and facets from mid November is buried 50 to 90cm deep. On Monday skier accidental and a skier remote triggered avalanche to size 2 were reported in Montana bowl.
Use extra caution at treeline where this layer is more prominent and look for signs of instability like shooting cracks, whumpfing and recent avalanches. Read our newest blog to learn more about this concerning layer and how to manage it.
Aspects: All aspects.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
Storm Slabs
Warmer temperatures have settled 30 - 50 cm of snow into a cohesive slab above a weak layer of 5mm surface hoar.
In the alpine southwest winds have pressed surfaces and built deep pockets in lees. As winds begin to blow from the north watch for reverse loading and cross-loading.
Don't forget that storm 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 13th, 2022 4:00PM
