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Avalanche Forecast

Archived

Nov 29th, 2021–Nov 30th, 2021

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Purcells.

New snowfall amounts will vary across the region on Tuesday. If you see less than 25 cm in your local area the avalanche danger is CONSIDERABLE.  

Confidence

Moderate - Uncertainty is due to the timing, track, & intensity of the incoming weather system.

Weather Forecast

The Interior regions will see the effects of the next atmospheric river by Tuesday. Precipitation will fall as snow at upper elevations and rain lower. Strong to extreme southwest wind will exist and freezing levels will be on the rise from 1400 m to 2500 m Tuesday night through Wednesday.

Monday Night: Periods of snow 5-10 cm. Alpine temperature -4 and freezing level 1500 m. Strong southwest wind.

Tuesday: Snow 10-20 cm at upper elevations. Alpine temperatures near -2 and freezing level 1800 m. Strong to extreme forecast southwest wind.

Wednesday: Heavy snow at upper elevations 20-30 cm. Alpine temperatures near -4 and will slowly climb to 0 degrees in some areas. Freezing level rising to 2300 m. Strong southwest wind.

Thursday: Snow continues 5-10 cm. Alpine temperatures near -4 and freezing level dropping to 1400 m. Strong southwest ridgetop wind. 

Avalanche Summary

Natural avalanche activity will be on the rise Tuesday with new snow, rain, wind, and rising freezing levels. Pay attention to your localized weather observations as the snow amounts differ across the region. Generally, if you see more than 25 cm and wind consider the hazard to be HIGH. It looks like the Dogtooth Range may see the least amount of snow which may keep the danger at CONSIDERABLE.

On Sunday numerous natural avalanches up to size 2 were observed in the Toby creek drainage. These avalanches ran on a surface hoar layer believed to be widespread in this area above 1600m. Several storm slab avalanches up to size 1.5 were observed in the Northern part of the range.

Snowpack Summary

New storm slabs will build with the incoming snow and bury recent wind slabs found at the treeline and the alpine. A surface hoar layer has been observed down 30 to 40cm in the Toby Creek drainage. The mid-November rain crust is throughout the region and down 30 to 60cm. It generally exists below 1900 m. Several early season crusts exist throughout the lower pack and a late October facet/crust layer sits at the bottom of the snowpack above 1900 m. Warm moist snow exists at lower elevations.

Average snowpack depth at treeline is 100cm to 180cm, with the deepest snowpack found around the Bugaboos.

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
  • Make conservative terrain choices and avoid overhead hazard.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.