Avalanche Forecast
Issued: Nov 29th, 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.
dboucher,
Avalanche Canada
Another atmospheric river storm will bring lots of precipitation and rising freezing levels. As a result, expect to see a widespread avalanche cycle with the potential for large, full-path avalanches. Avoid all avalanche terrain.
Summary
Confidence
Weather Forecast
The third of a series of atmospheric river winds its way down the BC coast. By Tuesday morning all coastal ranges will be in the throes of another torrential rain situation.
Monday night: Flurries; 10-15 cm. Strong to extreme southwest winds. Alpine low temperatures -3 C with freezing levels at 1500 metres.
Tuesday: Periods of snow mixed with rain; 15-30 cm and even more overnight. Extreme southwest winds. Alpine high temperatures -1 C with freezing levels at 1700 metres then peaking overnight at 2200 metres in the north of the region and 3000 m in the south of the region.
Wednesday: Snow, heavy at times mixed with rain; 10-20 cm. Moderate to extreme southwest winds.Alpine high temperatures +2 C with freezing levels at 2000 metres.
Thursday: Mainly cloudy with scattered flurries; 5 cm. Moderate southwest winds. Alpine high temperatures -7 C with freezing levels at 800 metres.
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 neighboring Sea to Sky. With another atmospheric river storm affecting the area Tuesday and Wednesday, expect to see a widespread avalanche cycle with the potential for large, full-path avalanches.
Snowpack Summary
Recent snowfalls and strong southerly winds continue to develop storm slabs in the alpine and at treeline with ticker accumulations in leeward features. All this new snow sit over a layer of surface hoar down 70-100 cm and a deeper crust / facets combo 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
Snowfalls at higher elevations are developing storm slabs that are likely to be thicker in lee terrain features. 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 on the deeper combo crust / facets.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
A deep weak layer affecting alpine areas could 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: Nov 30th, 2021 4:00PM
