Avalanche Forecast

Issued: Feb 21st, 2021 4:00PM

The alpine rating is high, the treeline rating is high, and the below treeline rating is high. Known problems include Storm Slabs and Persistent Slabs.

Avalanche Canada ahanna, Avalanche Canada

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Heavy overnight snowfall and cranking wind are a recipe for HIGH avalanche danger. Minimize your exposure to avalanche terrain Monday.

Summary

Confidence

High - We are confident a natural avalanche cycle will begin shortly after the arrival of the incoming weather.

Weather Forecast

SUNDAY NIGHT: 10-25 cm of new snow, strong to extreme westerly wind, freezing level 1500 m.

MONDAY: Around 5 cm of new snow, moderate to strong westerly ridgetop wind, freezing level 1300 m.

TUESDAY: Mix of sun and cloud, moderate westerly wind, freezing level 800 m.

WEDNESDAY: Mix of sun and cloud, moderate westerly wind, freezing level 1000 m.

Avalanche Summary

A size 1.5 loose dry avalanche was reported Friday out of steep rocky terrain near Valemount. With mind temperatures and cranking overnight winds, increased storm slab activity is expected at all elevations Monday. 

Last week, older winds slabs in cross and reverse-loaded terrain features surprised a number of skiers, triggering avalanches up to size 2.5. This surprisingly large human triggered avalanche was reported on a northwest facing feature at treeline.

Snowpack Summary

10-25 cm of new snow is forecast to fall overnight. Recent snowfall amounts have been highest in the south of the region near Blue River, where current storm totals are in excess of 100 cm as of Sunday morning! Other areas have received as little as 20 cm since the cold snap. At upper elevations, all of this recent snow will be easily blown around by strong to extreme westerly winds, forming thick, reactive slabs in lee features. At lower elevations, this recent low density snow is likely settling and gaining slab property in the warm temperatures. 

Below sits the old, facetted and/or extensively wind affected snow that sat on the surface during the extended cold, windy drought period. There is uncertainty around the strength of this interface with the new snow, which will surely be tested by the ongoing loading.

We've now got 40 to 80 cm of snow above the early February persistent weak layer which is composed of surface hoar. This layer is most prevalent at treeline and in "treeline-like" features like cutblocks. On steep south-facing terrain, this layer may consist of facets on a sun crust. 

Terrain and Travel

  • Use increased caution at all elevations. Storm snow is forming touchy slabs.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Stick to simple terrain features and be certain your location isn't threatened by overhead hazard.

Problems

Storm Slabs

An icon showing Storm Slabs

30-100 cm of recent storm snow continues to accumulate and settle into a slab in the mild temperatures. This storm slab sits overtop a thick layer of weak, sugary facets. At upper elevations, the recent snow will be easily blown around by strong to extreme westerly winds, forming thick, reactive slabs in lee features.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Almost Certain

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs

A persistent weak layer buried 40 to 80 cm deep has produced recent large avalanches and is expected to become increasingly reactive this weekend. This layer has been most sensitive around treeline, but may also extend into alpine terrain and/or down into the trees.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 3

Valid until: Feb 22nd, 2021 4:00PM

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