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Avalanche Forecast

Archived

Nov 22nd, 2020–Nov 23rd, 2020

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

Regions

Little Yoho.

Potential still exists to trigger wind slabs on steep alpine features like convex roll overs and couloirs. Conditions appear to be improving but step out with forethought and careful consideration.

Weather Forecast

Seasonal temperatures will persist in the region for the next 3 days. The valley will be near zero, with the ridge line being about -10. Upper level winds are expected to drop significantly tomorrow, with calm conditions up high. This will be disrupted by a once again strong wind pattern from the SW on Tues. Snow arriving again late Tuesday.

Snowpack Summary

Wind slabs present at treeline and above from W-SW winds. At treeline 20-50 cm of storm snow sits over a layer of preserved stellars. The Nov. 5 facet/crust combo is down 50-80 cm and producing variable test results from easy to hard. The Nov crust extends up to 2500 m on N aspects and higher on solar aspects. Snow depths at treeline are 50-130 cm.

Avalanche Summary

Today's field team, was near Bow Summit today. No avalanches were observed or reported in that area. Sunshine ski patrol, however, did report a size 2.5 avalanche that ran near the ground, likely yesterday, but was observed today. Control work at Sunshine produced avalanches up to size 1.5, in the form of wind slabs.

Confidence

Due to the number and quality of field observations on Sunday

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.