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Avalanche Forecast

Archived

Dec 7th, 2020–Dec 8th, 2020

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

Regions

South Columbia.

Avalanche danger will rise as snowfall continues through the day. The new snow is not expected to bond well to old surfaces. Watch for signs of instability like shooting cracks and be especially wary of wind loaded features where new snow may be sitting on crust or surface hoar.

Confidence

Moderate - We are confident a natural avalanche cycle will begin shortly after the arrival of the incoming weather.

Weather Forecast

The storm will deliver the bulk of its goods over the day Tuesday. Hot spots will be along the northern border of the region overnight Monday and the ranges on either side of upper arrow lake. Southern areas will see lighter snowfall amounts.

Monday night: 10-20 cm new snow, moderate southwest wind, freezing level 700 m.

Tuesday: 20-30 cm of new snow, moderate southwest wind, freezing level 900 m.

Wednesday: 5-10 cm new snow, light west wind, freezing level 1000 m.

Thursday: Flurries, light northwest wind, freezing level 700 m.

Avalanche Summary

A natural size 2 loose wet avalanche was observed on a south aspect in the alpine in Kokanee area on Sunday.

On Tuesday, we expect storm slabs to be touchy to natural and human triggers. You may see wide propagation especially on convexities around treeline and below. You'll likely see some loose dry sluffing out of steep terrain and under your skis.

Our eyes and ears in the mountains are limited this winter due to fewer professional observations. If you go out in the mountains, please share your observations on the Mountain Information Network (MIN). Photos are especially helpful! Thank you so much for all the great MINs submitted so far!

Snowpack Summary

20-30 cm of new snow over the day Tuesday will bring storm totals to 30-50. The storm snow sits ontop of a melt-freeze crust on south aspects and widespread surface hoar treeline and below. Generally speaking, new snow does not bond well to these types of surfaces.

The lower snowpack is characterized by a couple of crusts, the most notable of which is sitting near the base of the snowpack, likely surrounded by a weak layer of sugary facets. It does not appear to be a concern at this time.

Terrain and Travel

  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Be aware of the potential for large avalanches due to the presence of a deep persistent slab.
  • Choose conservative terrain and watch for clues of instability.

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.