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 for the next days.
Summary
Confidence
High - We are confident the likelihood of avalanche will increase with the arrival of the forecast weather.
Weather Forecast
The third of a series of atmospheric river winds its way down the BC coast and the Sea to Sky ranges will see rain ramp up through this afternoon and evening. Â
Monday night: Periods of snow; 20-35 cm. Strong southwest winds. Alpine low temperatures -4 C with freezing levels at 1300 metres.
Tuesday: Heavy snow changing to rain in the afternoon; 30-50 cm with even more overnight. Strong to extreme southwest winds. Alpine high temperatures +1 C with freezing levels at 2000 metres.
Wednesday: Wet snow mixed with rain; 30-40 cm. Strong to extreme southwest winds. Alpine high temperatures +2 C with freezing levels at 2200 metres.
Thursday: Mainly cloudy with scattered flurries; 5 cm. Moderate westerly winds. Alpine high temperatures -7 C with freezing level at 800 metres.
Avalanche Summary
Numerous natural and triggered avalanches, including large storm slabs avalanches (size 3 and 4) sliding on buried surface hoar and deeper buried crusts, have been reported Saturday during last storm. 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 are developing reactive storm slabs with thicker accumulations in leeward alpine and treeline features. This new snow continues to bury a surface hoar layer and a combo of thick crust / facets observed 50-100 cm down the surface in the alpine and at treeline. Surprising large avalanches sliding on these weak layers have been reported over the last few days. Heavy loading coming with this intense storm will likely produce more avalanche activity on these layers.
Average snow depths at treeline are now likely closer to 150-200 cm; 250+ cm in the alpine. Snowpack depths decrease dramatically below treeline and may still be below threshold for avalanches in some areas. Early season hazards such as rocks, stumps, and creeks are still a concern at these lower elevations.
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
Heavy snowfalls at higher elevations are developing storm slabs that are likely to be thicker in lee terrain features. More 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
