Avalanche Forecast

Issued: Dec 15th, 2022 4:00PM

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

Avalanche Canada ahanna, Avalanche Canada

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We have uncertainty around the reactivity of a buried weak layer that produced large rider-triggered avalanches last weekend. Read our latest blog for advice on how to manage a persistent slab problem.

Summary

Confidence

Low

Avalanche Summary

In the past week, we've had multiple reports of persistent slab avalanches on a buried weak layer. On the weekend, two skier-triggered size 2 avalanches were reported ~40 cm deep at treeline near Golden. Otherwise, persistent slab avalanches throughout the region have been mostly explosive controlled, size 1-2.

In the neighboring central Columbia and west Kootenay regions, where it is buried deeper, this layer has produced several alarming rider-triggered avalanches. Unfortunately, more likely than not, this is a sign of what is to come for the Purcells.

Snowpack Summary

Variable surfaces range from hard old wind slabs at wind exposed elevations to soft, unconsolidated facets in sheltered areas.

A concerning weak layer composed of surface hoar, facets and/or a crust that formed in mid November is now buried 15-40 cm deep. Avalanche activity has been observed on this layer and is expected to continue as the overlying snow takes on more slab character due to settlement, wind and additional snow load.

Alpine snowpack distribution is variable, with depths ranging from 40 to 140 cm.

Weather Summary

Thursday night

Increasing cloud. Light northwest wind. Alpine low -13 C.

Friday

A mix of sun and cloud. Moderate northwest ridgetop wind. Alpine high of -10 C.

Saturday

Scattered flurries bringing a trace of snow. Light to moderate northwest wind. Alpine high of -12 C.

Sunday

Scattered flurries bringing a trace of snow. Light to moderate southwest wind. Alpine high of -20 C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • In times of uncertainty conservative terrain choices are our best defense.
  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • Avoid open slopes and convex rolls at and below treeline where weak layers may be preserved.
  • Be carefull around freshly wind loaded features.

Problems

Persistent Slabs

An icon showing Persistent Slabs

A buried weak layer composed of surface hoar and facets has produced surprising skier-triggered avalanches in the past week. Avalanches are most likely to be triggered on this layer in areas around treeline.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 2.5

Wind Slabs

An icon showing Wind Slabs

As ridgetop winds pick up today from the northwest, any loose surface snow will be transported into fresh wind slabs in atypical terrain features due to reverse-loading.

Aging wind slabs formed by previous southwest wind may remain reactive to human triggers, especially where they overlie a weak, sugary lower snowpack.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

1 - 1.5

Valid until: Dec 16th, 2022 4:00PM