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Avalanche Forecast

Archived

Dec 28th, 2019–Dec 29th, 2019

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Purcells.

Very large recent avalanches have run to valley bottom, extended avalanche paths & taken out trees. This is the time to make conservative choices, stick to simple terrain and always be aware of what terrain is above you.

Confidence

Moderate - Uncertainty is due to the fact that deep persistent slabs are particularly difficult to forecast.

Weather Forecast

Saturday night: Scattered cloud, low -12 C, alpine wind light to moderate northwest.

Sunday: Mostly sunny, alpine high -7 C, alpine wind light northeast.

Monday: Scattered cloud increasing overnight, alpine high -6 C, alpine wind northwest building to strong through the day.

Tuesday: Mostly cloudy with isolated flurries, alpine high -6 C, alpine wind moderate to strong northwest.

Avalanche Summary

Avalanche activity in the Purcells this week is simultaneously impressive and terrifying. Explosive control work in the central portion of the region continues to produce large persistent slab avalanches size 3 and larger on all aspects in alpine terrain. Common characteristics include wide propagation, remote triggers and full depth avalanches running to ground. Natural avalanches of similar scale have been reported as recently as Friday.

Earlier in the week, there were several instances of large natural events taking out old timber beyond historical avalanche boundaries and running from the high alpine all the way to valley bottom.

Snowpack Summary

The Purcells received 60-120 cm from last weekend's big storm which has been settling into a slab over a couple of buried surface hoar layers 70-180 cm below the surface. This is normally a recipe for a concerning persistent slab avalanche problem in its own right, but there's more to the story...

The base of the snowpack is astonishingly weak, far more so than in the average season. This weakness is widespread across aspects and elevation bands meaning it's almost everywhere. It consists of crust, facets and depth hoar. With the addition of the new snow last weekend, this weakness became overloaded and its failure has resulted in some spectacularly large and destructive avalanche activity.

Terrain and Travel

  • Don't let the desire for deep powder pull you into high consequence terrain.
  • Stick to simple terrain and be aware of what is above you at all times.
  • Very large and destructive avalanches could reach valley bottom.
  • Be aware of the potential for surprisingly large avalanches due to deeply buried weak layers.