Avalanche Forecast
Issued: Dec 10th, 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.
astclair,
Avalanche Canada
Heavy snowfall and strong wind are creating very dangerous avalanche conditions. Having the skills to recognize and avoid avalanche terrain will be critical to managing your risk on Saturday. Stick to simple, low-angle slopes with no overhead hazard.
Summary
Confidence
Weather Forecast
An intense Pacific front plows through on Saturday and hammers the region with snow and wind
Friday night: Cloudy, 5-15 cm of snow, strong southwest wind, treeline temperatures rising to -4 C overnight, freezing level rising to 1200 m.
Saturday: Cloudy, 5-15 cm of snow, strong southwest wind, treeline temperatures dropping to -8 C, freezing level dropping to valley bottom by end of day.
Sunday: Mainly cloudy, up to 5 cm of snow, moderate southwest wind, treeline temperatures near -10 C, freezing level around 500 m.
Monday: Mix of sun and cloud, isolated flurries with up to 5 cm of snow, light winds becoming east, treeline temperatures near -8 C, freezing level around 500 m.
Avalanche Summary
We expect that natural and human triggered avalanches will release large and run far during the storm.
Snowpack Summary
A potent storm with strong wind is forecast to bring 15-30 cm of new snow to the mountains by the end of Saturday, favoring areas south in the region near Allison Pass. This will create a widespread, reactive storm slab problem that will be particularly pronounced where the snow is drifted by southwest winds. The snowpack will need time to adjust to this rapid load. Closely monitor how the new snow is bonding to the old surface as the cold snow is not expected to bond well to previous snow surfaces.
In the north of the region, the snowpack near upper treeline elevations is complex and warrants conservative route selection. Weak faceted snow can be found near two possible crust layers that formed in early December, which may become reactive with loading from new snow. Our models suggest that this layer may be most pronounced at elevations between 1400-1800 and in areas north in the region, like the Hurley.
The south of the region has seen substantially higher snow totals over the past week, with some areas seeing 50+ cm. Expect to find deeper snow accumulations above the December crust and anticipate larger, more reactive storm slab avalanches.
Having endured warmer temperatures and more rainfall, the southern part of the region is just reaching the threshold for avalanches at most elevations.
Terrain and Travel
- Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
- Expect slab conditions to change drastically as you move into wind exposed terrain.
- Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
- Be aware of the potential for large avalanches due to the presence of a persistent slab.
Problems
Storm Slabs
New snow with strong wind is forming widespread, reactive slabs. Expect this problem to be more pronounced in wind-drifted areas. Closely monitor how the new snow is bonding to the old surface, and back off terrain where you see more than 25 cm of new snow.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
In the north of the region, a layer of weak facets (sugary snow) can be found near crust layers that formed in early December. It is possible that this facet-crust combination will react as a persistent slab problem with rapid loading from new snow. This potential persistent slab problem warrants diligent, conservative route selection at treeline elevations. Avoid open slopes and convex rolls near treeline where weak layers may be preserved.
Aspects: All aspects.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
Valid until: Dec 11th, 2021 4:00PM
