Avalanche Forecast

Issued: Feb 21st, 2021 4:00PM

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

Avalanche Canada shorton, Avalanche Canada

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Overnight snowfall and strong wind will create very dangerous avalanche conditions at upper elevations.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

A cold front crossing Sunday night will bring decent snow accumulations to higher elevations before it clears and cools.

SUNDAY NIGHT: 30-40 cm of snow near the coast and 15-25 cm near Whistler and Pemberton, strong southwest wind, freezing level around 1300 m with treeline temperatures around -2 C. 

MONDAY: Clearing skies and dropping temperatures in the morning, moderate gusts from the west, freezing level dropping to 500 m as treeline temperatures drop to -5 C.

TUESDAY: Mix of sun and cloud, light wind, treeline temperatures around -8 C.

WEDNESDAY: Mostly sunny, light wind, treeline temperatures around -8 C.

Avalanche Summary

Periods of heavy snowfall and wind will likely drive a natural avalanche cycle on Sunday night, while lower elevations may experience wet loose avalanches triggered by the rain. Preliminary reports from Sunday suggest the first 15 cm of storm snow was reactive to human triggering, and these reactive storm slabs will get thicker overnight. Natural and human triggered avalanches will remain likely at treeline and alpine elevations across many parts of the region on Monday.

Snowpack Summary

Forecast snowfall amounts are variable across the region with 40 cm expected in coastal areas like Squamish and the Sunshine Coast and closer to 20 cm further inland near Whistler and Pemberton. The new snow and wind will form reactive slabs above the rain line. Recent snow is sitting above a potentially reactive interface consisting of surface hoar layer at treeline, a crust below 1800 m, sun crusts on steep south slopes, and faceted surfaces in the alpine. These interfaces could be failure layers for storm slabs.

A lingering persistent weak layer from late January is 80-120 cm deep and consists of facets at upper elevations and surface hoar in sheltered areas. Although this structure is suspect, we have no recent reports of avalanches on this layer.

Terrain and Travel

  • Avoid all avalanche terrain during periods of strong wind.
  • Stick to simple terrain features and be certain your location isn't threatened by overhead hazard.
  • Dial back your terrain choices if you are seeing more than 20 cm of new snow.

Problems

Storm Slabs

An icon showing Storm Slabs

Storm slabs will be very reactive to human triggering on Monday with 20-40 cm of fresh snow expected. Natural avalanche activity will be likely in alpine and treeline terrain, especially in heavier snowfall areas near the coast. Strong to extreme wind will be the main driver of natural avalanche activity.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 2.5

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