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. 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 night, with increased amounts in the Monashees. Arctic air will return on early Friday, with bitterly cold and drier conditions for the weekend.
TUESDAY NIGHT: Snow 5-10 cm / Strong to extreme southwest wind / Low of -12
WEDNESDAY: Snow 10-15 cm / Strong to extreme southwest wind / High -8Â
THURSDAY: Snow 5-10 cm/ Moderate to strong west wind / High of -10
FRIDAY: Flurries 5 cm / Moderate southwest wind / High of -15
Avalanche Summary
Few natural dry loose avalanches were reported out of steep terrain (size 1) as well as numerous fresh wind slab avalanches out of alpine convexities. 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
Strong wind has affected the recent storm snow (30-40 cm) in upper elevation only and scouring some southerly alpine features. Meanwhile, cold temperature was prone to develop weak surface snow grains, such as surface hoar, in sheltered areas at treeline elevation and below.
The defining feature of the snowpack is a widespread crust that reaches as high as 2200 m and now sits 80-150 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 facets above the crust are 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 shallow snowpack areas, rock outcroppings and steep convex terrain where triggering is most likely.
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 80-150 cm near a crust layer that formed in early December. Although this persistent weak layer has not shown recent reactivity where it is buried over a meter, the likelihood of triggering it will increase with the incoming storm. Avoid likely trigger spots such as steep, convex slopes, with a shallow or thin to thick snowpack, especially at treeline.
Aspects: All aspects.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
Valid until: Dec 22nd, 2021 4:00PM
