Avalanche Forecast

Issued: Dec 13th, 2021 4:00PM

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is low. Known problems include Wind Slabs and Persistent Slabs.

Avalanche Canada TRettie, Avalanche Canada

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 Continually assess for changing snowpack conditions. Variable wind direction and the presence of a persistent weak layer make for challenging decision making.  

Summary

Confidence

Moderate -

Weather Forecast

Monday night: light to moderrate Southeast winds with some flurries bringing up to 10cm of new snow. Temperature at 1500m will be -8.

Tuesday: 10 to 20cm of new snow with the higher accumulations in the South part of the forecast region. Winds in the alpine will be light to moderate from the Southwest. A high of -7 is expected at 1500m.

Wednesday: Mostly cloudy. Light southerly wind. High of -7 at 1500m..

Thursday: High of -8 at 1500m. Up to 10cm of new snow with winds becoming strong from the Nrthwest.

Avalanche Summary

Several natural and skier triggered wind slabs on North and East aspects were reported up to size 2 on Sunday. These avalanches were all in terrain above 1900m.

A noteworthy event from the east slopes of the Selkirks, a size 3 (very large) avalanche was triggered by a skier on a cross-loaded south aspect, resulting in a 300 m ride and partial burial. This avalanche is suspected to have run on the crust described in the snowpack summary.

Snowpack Summary

15-30 cm of recent snow has been redistributed by moderate to strong wind from the Southwest.  

The defining feature of the snowpack is a widespread prominent crust that reaches as high as 2200 m in the alpine now sits 50-80 cm below the surface. In many places, overlying snow is well-bonded to the crust but in others, weak faceted grains have been observed growing above it around treeline. Snowpack models show the faceting process progressing quickly at this elevation, likely due to the amount of heat and moisture trapped by the crust. We will be closely monitoring this layer going forward. The snowpack structure is relatively simple beneath the crust. with treeline snowpack depths 150-200 cm.

Terrain and Travel

  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
  • Approach lee and cross-loaded slopes with caution.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Avoid open slopes and convex rolls at and below treeline where weak layers may be preserved.

Problems

Wind Slabs

An icon showing Wind Slabs

Small inputs of new snow will continue to feed wind slabs. As wind direction shifts southeast on Monday, watch for changes in loading patterns.

Aspects: North, North East, East, South East, West, North West.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs

50-80 cm of snow sits over a weak layer on a thick crust. While only a handful of avalanches have been reported to have run on this layer, they have been large. Avalanches on this layer may be triggered by humans or vehicles from thin spots or by large loads like wind slab avalanches.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Possible

Expected Size

2 - 3

Valid until: Dec 14th, 2021 4:00PM