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Avalanche Forecast

Archived

Dec 13th, 2021–Dec 14th, 2021

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

Regions

Little Yoho.

The danger continues to come down following the last storm, but we expect windslabs remain in high alpine areas (where we have no observations). Cold temperatures, light winds and soft surface snow have created excellent backcountry conditions.

Weather Forecast

A Pacific weather system moves into the region this evening and will deposit 5-10 cm along with moderate S winds and temperatures remaining in the -5 to -15 range. This storm will clear by late day on Tuesday when a ridge of high pressure clears the skies for mid-week.

Snowpack Summary

20-30 cm of low density snow surface snow is bonding well with only limited windslab development at treeline and the low alpine. Our concern is growing for weaknesses developing above the Dec 2 rain crust, now buried 60-80 cm at treeline elevations (below 2250). Watch carefully as this weakness develops into an avalanche problem in the coming days.

Avalanche Summary

No new natural avalanches have been reported. Both LL and SSV ski areas report windslabs up to size 1 in their alpine areas. SSV noted several avalanches up to size 2 failing on the Dec 2 layer and propagating up to 40 meters wide by 70 cm deep fractures - these are the first avalanches we have seen on the Dec 2 layer.

Confidence

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.