Avalanche Forecast
Issued: Dec 21st, 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.
jleblanc,
Avalanche Canada
Watch the winter storm carefully as storm slabs will develop throughout the day. Areas in the west of the region are the most likely to see high snowfall amounts.
Summary
Confidence
Moderate - Uncertainty is due to how the snowpack will react to the forecast weather.
Weather Forecast
A unique situation of weather setting up as two systems, one from the north and one from the south, will push into the region early Tuesday evening through late Thursday, with increased amounts in the Monashees. Arctic air will return on early Friday, with bitterly cold and drier conditions for the weekend.
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TUESDAY NIGHT: Snow 5-10 cm / Strong southwest wind / Low of -13Â
WEDNESDAY: Snow 10-15 cm / Strong to extreme southwest wind / High -8
THURSDAY: Snow 10 cm / Moderate west wind / High of -12
FRIDAY: Flurries 5 cm / Moderate southwest wind / High of -15
Avalanche Summary
Few natural wind slab avalanches (size 1.5) released out of alpine convexities. Riders were also able to trigger soft slabs while skiing steep lee slopes at treeline elevations. With the next storm, the likelihood of avalanches will increase in many areas.
If you go out in the mountains, please consider filling out a Mountain Information Network report.
Snowpack Summary
Variable wind has affected the storm snow (20-35 cm) on alpine and treeline slopes, creating isolated small pockets of hard/firm slabs. Cold temperature was prone to develop weak surface snow grains, such as surface hoar, in sheltered areas at treeline elevation and below.Â
The defining feature of the snowpack is a widespread crust that reaches as high as 2400 m and now sits 60-150 cm below the surface. In some places, overlying snow is well-bonded to the crust but in others, weak faceted grains have been observed above it. The faceting is most prominent at treeline where the crust is thinner. In areas where the crust is buried deeper than one meter, it starts to decompose and show sporadic reactivity.
Terrain and Travel
- Storm slab size and sensitivity to triggering will likely increase through the day.
- Continue to make conservative terrain choices while the storm snow settles and stabilizes.
- If triggered, storm slabs in-motion may step down to deeper layers and result in very large avalanches.
- Avoid rock outcroppings, convexities, and anywhere the snowpack is thin and/or variable.
Problems
Storm Slabs
Expect storm slabs to build at all aspects / elevations, especially behind lee features, throughout the day Wednesday as consistent snowfalls will impact the region. Increased amounts are expected in the Monashees with this strong southwesterly flow.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
A layer of weak facets (sugary snow) can be found down 60-150 cm near a crust layer that formed in early December. Although this persistent weak layer hasn't recently shown reactive, the likelihood of triggering it will increase with the incoming storm at treeline elevations. Avoid likely trigger spots such as steep, convex slopes, with a shallow or thin to thick snowpack.
Aspects: All aspects.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
Valid until: Dec 22nd, 2021 4:00PM
