Dashboard Regions Weather Stations Radar Alerts Glossary
Contact About
Log In

Register for an account and never miss a forecast again!

Register

Avalanche Forecast

Archived

Nov 30th, 2020–Dec 1st, 2020

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

North Rockies.

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.

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

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.