Avalanche Forecast

Issued: Nov 30th, 2020 4:00PM

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

Avalanche Canada MBender, Avalanche Canada

Email

Wind slabs are the main concern on Tuesday as the wind continues to redistribute recent new snow onto protected slopes. Above freezing temperatures at upper elevations on Wednesday are expected to keep the avalanche danger elevated.

Summary

Confidence

Low - Uncertainty is due to limitations in the field data. Uncertainty is due to rapidly fluctuating freezing levels.

Weather Forecast

MONDAY Night: Clear periods / Moderate west wind / Alpine temperature around -6 C.

TUESDAY: Mix of sun and cloud / Moderate south wind / Alpine temperature around -3 C / Freezing level rising to 1500 m in the afternoon.

WEDNESDAY: Mainly sunny / Moderate south wind / Alpine temperature around 3 C / Freezing level 2500 m.

THURSDAY: Mainly sunny with cloudy periods / Light southwest wind / Alpine temperature around -4 C / Freezing level 500 m.

Avalanche Summary

There has been a report of an avalanche fatality near Pine Pass on Saturday. Reports indicate a size 3 deep persistent slab avalanche at approximately 1600 m elevation on a northeast aspect. The avalanche was approximately 55 cm deep, 800 m wide and ran 400 m in length. The avalanche was possibly remotely (triggered from a distance) and may have run on a weak layer of faceted crystals sitting on a crust that was buried in early November.

Snowpack Summary

Snow depths are approximately 150 cm in the north west of the region (Pine Pass), 180 cm in the south (Renshaw, Kakwa) and 100 cm in the the north east (Tumbler ridge).

In the deeper areas, successive storms have resulted in deep powder in the upper snowpack. The wind is changing that because it will certainly be blown into denser wind deposits. The question is whether windward slopes will become stripped of the recent snow.

Most likely the most significant instabilities are within or at the base of the most recent storm snow, approximately 50-70 cm below the snow surface.

A crust forming in early November is near the base of the snowpack. In some areas facets have been reported sitting on this crust. This layer is of most concern on steep terrain in thinner snowpack areas.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Extra caution for areas experiencing rapidly warming temperatures for the first time.
  • Be aware of the potential for large avalanches due to the presence of a deep persistent slab.
  • Avoid steep convexities or areas with a thin, rocky, or variable snowpack.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

Problems

Wind Slabs

An icon showing Wind Slabs

30-70 cm of snow fell late last week with the highest amounts in the south. Strong southwest winds have built deep wind slabs at treeline and alpine elevations on lee and crossloaded slopes. 

Aspects: North, North East, East, North West.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1.5 - 2.5

Deep Persistent Slabs

An icon showing Deep Persistent Slabs

There is currently 90-120 cm of snow sitting on top of weak a layer of sugary facets that developed above a firm crust which formed in early November. Warm temperatures at upper elevations late Tuesday and through Wednesday may increase the likelihood triggering deep persistent slabs.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 3

Valid until: Dec 1st, 2020 4:00PM

Login