Avalanche Forecast

Issued: Jan 3rd, 2021 4:00PM

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

Avalanche Canada shorton, Avalanche Canada

An intense storm has left dangerous avalanche conditions across the region. Avoid alpine avalanche terrain and choose lower angle slopes free from overhead hazards.

Summary

Confidence

High - We have a good understanding of the snowpack structure and confidence in the weather forecast

Weather Forecast

A brief lull between storms before the next system arrives on Tuesday.

SUNDAY NIGHT: Mostly cloudy, moderate south wind, treeline temperatures around-6 C.

MONDAY: Scattered flurries with 5-10 cm of snow with some localized heavier accumulations along the coast in the south (near Kitimat), strong south wind, treeline temperatures around -3 C.

TUESDAY: Flurries with 15-30 cm of snow, strong south wind, treeline temperatures around -3 C.

WEDNESDAY: Scattered flurries with 5-15 cm of snow, moderate southwest wind, treeline temperatures around -3 C.

Avalanche Summary

Widespread storm slab avalanche activity has been reported since New Year's Day, including numerous human triggered avalanches in the Shames area (see photos in MIN reports here and here). These size 1-1.5 slabs triggered on Friday were extra reactive above buried surface hoar and crust layers that were 30 cm deep at the time. These weak layers are now buried beneath 50-100 cm of storm snow, which creates the potential for large human triggered avalanches this week.

Preliminary reports suggest recent avalanches have only involved new storm snow, with the exception of a few explosive triggered avalanches that stepped down to deeper weak layers.

Snowpack Summary

Storm weather since New Year's has brought 50-100 cm of fresh snow and formed a widespread storm slab problem. Strong southwest wind has also formed thick reactive wind slabs in exposed terrain. Reports in the early stages of the storm suggest these slabs are very reactive and bonding poorly to crust and surface hoar layers. There are two weak layers of feathery surface hoar beneath recent storm snow, now an estimated 60-120 cm deep. The deeper surface hoar was reported as being widespread prior to burial and the upper layer may sit on a melt-freeze crust from warm air on Boxing Day and/or from sunny skies.

Around 150 to 200 cm deep, a hard melt-freeze crust from early December may have weak and sugary faceted grains around it. These weak layers are likely the culprit of avalanche activity last weekend in the Nass Valley, Sterling, and Beaupre riding areas.

The early-November melt-freeze crust is over 200 cm deep and may have faceted grains above it in parts of the region, particularly in the north. The last reported avalanche activity was near Ningunsaw on Dec 11.

Terrain and Travel

  • Avoid the alpine during periods of heavy loading from new snow wind and/or rain.
  • Choose simple, low-angle, well supported terrain without convexities.
  • Avoid exposure to overhead avalanche terrain, avalanches may run surprisingly far.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.

Problems

Storm Slabs

An icon showing Storm Slabs

50-100 cm of recent snow and strong wind has left widespread storm slabs that can easily be triggered by skiers and sledders. These slabs sit above several concerning weak layers (surface hoar and crusts). Strong wind on Monday creates the additional danger of natural avalanches in the alpine.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1.5 - 2.5

Persistent Slabs

An icon showing Persistent Slabs

Numerous weak layers may exist in the top half of the snowpack, including surface hoar and faceted grains over a melt-freeze crust. These layers were recently triggered in riding areas north of Terrace. The likelihood of avalanches involving these layers will be heightened during and immediately after this stormy period.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 3.5

Valid until: Jan 4th, 2021 4:00PM