Avalanche Forecast
Issued: Nov 30th, 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.
cgarritty,
Avalanche Canada
AVOID ALL AVALANCHE TERRAIN. A natural avalanche cycle is expected overnight Tuesday with very large avalanches running full path. Very dangerous conditions will persist through Wednesday.
Summary
Confidence
Weather Forecast
Tuesday night: Periods of snow and rain, Rain as high as 2300 metres. Strong to extreme southwest winds. Freezing level peaking at 2500 metres.
Wednesday: Continuing snowfall bringing 10-30 cm of new snow. Rain below about 1600 metres. Strong to extreme southwest winds. Treeline high temperatures around 0C with freezing levels between 1800-2000 metres.
Thursday: Mainly sunny. Light southwest winds. Treeline high temperatures around -7 with freezing levels back to 800 metres.
Friday: Initially clear but clouding over by afternoon. Light variable winds. Treeline high temperatures around -7.
Avalanche Summary
Large avalanches sliding on recently buried surface hoar and deeper buried crusts have been observed in the region as well as in the neighbouring Sea to Sky. With another atmospheric river storm continuing to pummel the region through Wednesday, we expect to see a widespread avalanche cycle with the potential for large, full-path avalanches.
Snowpack Summary
Heavy snowfall and strong southerly winds continue to develop storm slabs in the alpine and at treeline, with thicker accumulations in leeward features. All this new snow sits over a layer of surface hoar down 70-100 cm and a deeper crust/facet combo layer that produced large avalanches during Saturday's storm. Heavy loading and warming coming with this intense storm will likely produce more avalanche activity on these layers.
Average snowpack depths in the alpine are now 130-180 cm. Below treeline, depths of 30-50 cm have been reported around 500 m, decreasing dramatically with elevation, and still below threshold for avalanching in many areas. Early season hazards such as rocks, stumps, and creeks are a concern below the alpine.
Terrain and Travel
- Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
- If triggered, storm slabs in-motion may step down to deeper layers and result in very large avalanches.
- Be aware of the potential for large, deep avalanches to run full path or even longer.
Problems
Storm Slabs
Continuing snowfall at higher elevations is developing storm slabs that will be primed to release naturally or with a human trigger on Wednesday. More heavy loading and rising freezing levels with the ongoing storm will result in increasing avalanche activity. Avalanches have the potential to be larger than expected if they step-down to a deeper crust/facet layer. This layer was active even before the current storm.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
A deep weak layer affecting alpine areas is expected to result in very large, full-path destructive avalanches. Significant loading and rising freezing levels during the ongoing storm will likely produce more avalanche activity on this layer.
Aspects: All aspects.
Elevations: Alpine.
Likelihood
Expected Size
Valid until: Dec 1st, 2021 4:00PM
