Avalanche Forecast

Issued: Dec 23rd, 2020 4:00PM

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

swerner, Avalanche Canada

South Rockies.

Wind slabs will likely be reactive to human triggers on Thursday especially where they sit on a buried weak layer. Conservative terrain selection is crucial until we have good evidence that the layers have stabilized.

Summary

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

An upper ridge of high pressure will generally keep the region cool and dry through the forecast period. A temperature inversion may slightly warm ridgetop temps on Thursday.

Thursday/Friday: Mix of sun and cloud. Alpine temperatures near -2 and freezing levels 1500 m. Ridgetop wind moderate to strong from the southwest.

Saturday: Light snow 3-7 cm. Alpine temperatures -3 and freezing levels valley bottom. Ridgetop wind moderate from the southwest.

Avalanche Summary

Numerous natural wind slab avalanches up to size 2 were reported today from our field team. These were mostly seen from West aspects in the alpine.Â

On Tuesday widespread natural avalanche activity up to size 3 was reported through the region.

Natural avalanche activity may taper off a bit but the snowpack remains primed for human triggering.Â

Please consider sharing your observations on the Mountain Information Network. Thank you to those that have already submitted this winter!

Snowpack Summary

30-50 cm of recent storm snow blanketed the region by Tuesday morning. Storm slabs will likely be reactive to human triggers, especially where the wind stiffens the new snow. A persistent slab 70-110 cm thick now sits on the early December crust. This persistent weak layer, with facetted crystals and surface hoar crystals above and/or below it is reaching a tipping point.Â

The base of the snowpack consists of a hard melt-freeze crust from early-November that may also have weak crystals around it. This potential avalanche problem is dormant at this time, however; it remains on our radar. The most likely spot to trigger it would be on thin and rocky slopes or, like above, from step down avalanches in the recent storm snow.

Terrain and Travel

Shooting cracks, whumphs and recent avalanches are strong indicators of an unstable snowpack.
If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
Uncertainty is best managed through conservative terrain choices at this time.
Don't let the desire for deep powder pull you into high consequence terrain.

Problems

Wind Slabs

Wind slabs will likely be reactive on Thursday due to strong wind and lots of available snow to transport. Natural avalanches, whumphing, and shooting cracks in the snow are all indicators of a instability. Loose-dry sluffing from steep terrain is likely, especially when the sun comes out.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Persistent Slabs

This layer has reached a tipping point in parts of the region. 70-110 cm of snow currently sits above a weak layer from early December. Combinations of sugary facets , surface hoar and/or a crust mean persistent slabs are likely reactive, especially to human triggers.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 3.5

Valid until: Dec 24th, 2020 4:00PM