Avalanche Forecast
Issued: Dec 22nd, 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
The current storm will continue until Thursday evening. In areas where you see more than 30 cm new snow, increase the danger rating to HIGH.
Summary
Confidence
Weather Forecast
A unique situation of weather setting up as two systems, one from the north and one from the south, is pushing into the region through late Thursday night, bringing consistent snowfall amounts. Arctic air will return on early Friday, with bitterly cold conditions for the weekend.
WEDNESDAY NIGHT: Heavy snow 10-15 cm/ Strong to extreme southerly wind / Low -8
THURSDAY: Snow 10-15 cm/ Moderate to strong west wind / High of -10
FRIDAY: Flurries 5 cm / Light southwest wind / High of -15
SATURDAY: Flurries 5 cm / Light southwest wind / High of -18
Avalanche Summary
Few observations were reported Wednesday due to poor visibility. Wind slabs were reactive to skier traffic and were up to 40 cm in thickness. Natural dry loose avalanches (size 1.5 - 2) were also reported from low-density snow on steep slopes at treeline and below treeline.
If you go out in the mountains, please consider filling out a Mountain Information Network report.
Snowpack Summary
Touchy soft storm slabs are forming on slopes where accumulation are exceeding 30 cm. Recent strong alpine wind has created wind slabs in alpine and on cross-loaded features. Prior to this storm, cold temperature in the valley weak surface snow grains (surface hoar) were observed on isolated sheltered slopes at treeline and below.
A widespread crust, formed in early December, reaches as high as 2200 m and now sits 100-150 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
Continued precipitations will impact the region, intensifying Thursday morning. Expect reactive storm slabs to develop at all aspects / elevations, especially behind lee features. These slabs will be easily triggered by riders, especially in wind-affected areas. Increased snowfalls are expected in the west part of the region (35 cm +) 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 deeper than one meter, the likelihood of triggering it will increase with the current 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 23rd, 2021 4:00PM
