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Avalanche Forecast

Archived

Dec 11th, 2020–Dec 12th, 2020

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

Regions

Purcells.

Storm slabs may remain reactive where they sit over a crust or surface hoar.

Moderate danger below treeline reflects conditions around Golden. Avalanche danger at this elevation will be a step lower in other parts of the region where less than 15 cm of snow sits over the crust.

Confidence

Moderate -

Weather Forecast

Continued cool temperatures, with a mix of sun, clouds and snow flurries for the next few days as the next weak low pressure moves in Sunday.  

Friday Night: Clear with cloudy periods, light and variable winds, alpine low -13C, freezing level valley bottom. 

Saturday: Sun and cloud, light and variable winds, alpine High -10C in the north, -7C in the south, freezing level valley bottom.

Sunday: Cloudy with snow flurries, trace Accumulations 0-5cm, light-moderate southerly winds, alpine low -11/ high -8C, freezing level 700 m.

Monday: Cloudy with sunny periods & isolated snow flurries, light to moderate westerly winds, alpine low -11C / high -8C, freezing level 900 m.

Avalanche Summary

Explosive control work at Panorama on Thursday produced numerous size 1 storm slab avalanches on north aspects in the alpine. 

Natural, skier and explosive triggered storm slab avalanches up to size 2 were reported throughout the region during the storm Tuesday and Wednesday.

Have you been out and about in the mountains? If so please submit your observations to the Mountain Information Network (MIN). It doesn't have to be technical - photos are especially helpful! Thank you so much for all the great MINs submitted so far! 

Snowpack Summary

10-30 cm of recent snow overlies a rain crust found up to 2450 m in the south of the region and 1800 m in the north. In the north, the recent snow may sit over a weak layer of surface hoar or facets at elevations around treeline where this crust is not found or where it is a very thin lens that formed ontop of the surface hoar. The recent snow does not appear to be bonding well to these old surfaces.

The lower snowpack is characterized by a couple of crusts, the most notable is from a rain event in early November. This crust is sitting near the base of the snowpack, surrounded by a weak layer of sugary facets. It is most likely to be reactive to human triggers or in a step-down from a smaller avalanche in shallow, rocky areas.

Terrain and Travel

  • Keep in mind that human triggering potential persists as natural avalanching tapers off.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Brief periods of sun could quickly initiate natural avalanche activity.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.

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.