Avalanche Forecast
Issued: Jan 14th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
ahanna,
Avalanche Canada
New snow and wind will keep storm slabs and cornices fresh. As you tiptoe around these surface instabilities remember their potential, if triggered, to step down to persistent slab avalanches on deeply buried weak layers. Such avalanches have been large and destructive lately.
Summary
Confidence
Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.
Weather Forecast
Thursday night: Rain/wet snow, 10-20 mm/cm, strong south winds, freezing level fluctuating between 2000 and 1300 m.
Friday: Mix of sun and cloud, moderate west wind, freezing level 1300 m.
Saturday: Mix of sun and cloud, light southwest wind, freezing level 1300 m.
Sunday: Snow, 5-15 cm, moderate southwest wind, freezing level 1200 m.
Avalanche Summary
On Wednesday, there were reports of a natural storm slab avalanches cycle up to size 3. There were also several that stepped down to deeper weak layers resulting in very large (size 3-4) persistent slab avalanches. Check out this MIN describing a large cornice-triggered avalanche in the Blackcomb sidecountry.
Last Saturday, a large (size 3) avalanche was remotely triggered by skiers on Cowboy Ridge near Whistler. The avalanche occurred on a north to northwest aspect at around 1900 m. The crown ranged reached up to 200 cm and was approximately 200 m wide. Check out this MIN for photos and more information. A similar avalanche was remotely triggered by skiers on a nearby westerly slope a few days before; check out this MIN for more info and photos.
Snowpack Summary
40-60 cm of recent storm snow accompanied by strong to extreme westerly wind has built reactive storm and wind slabs at upper elevations. These slabs may be extra sensitive where they overlie surface hoar in sheltered terrain or a crust on solar aspects. Warmer temperatures and a period of rain overnight Tuesday has formed a thin surface crust up to 1900 m.
The snowpack is currently quite complex. Layers of surface hoar as well as sugary faceted grains above a hard melt-freeze crust from early December may be found down 100 to 200 cm. Last weekend, several large natural and human-triggered avalanches on this layer occurred, with the hot spots being around the Whistler backcountry.
Near the base of the snowpack, there may be faceted grains above a crust from early-November, which was identified as the failure layer in recent sporadic large avalanche releases.
Terrain and Travel
- In times of uncertainty conservative terrain choices are our best defense.
- Cornice failure may trigger large avalanches.
- Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
Problems
Storm Slabs
New and reactive storm and wind slabs are expected to linger after the storm. Strong to extreme southwest wind will persist depositing recent snow into deeper slabs on leeward slopes in the alpine. Cornices have grown large and may be fragile. They deserve respect and a wide berth from below and above.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
A couple of problematic layers may be found around 100 to 200 cm deep, including weak layers of surface hoar and faceted grains above a hard melt-freeze crust. A few high-consequence avalanches have been triggered by riders in the past few days near Whistler.
Read what a local guide has to say about these persistent weak layers here.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Jan 15th, 2021 4:00PM
