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Avalanche Forecast

Archived

Nov 24th, 2019–Nov 25th, 2019

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

Regions

Little Yoho.

Natural avalanche activity will decrease on Monday but human triggering of wind slabs will remain likely. Use caution or avoid fresh wind loaded areas and narrow gullies until the new snow has had a chance to settle and bond.

Weather Forecast

Winds will stay out of the west but start to decrease on Monday to the moderate range. Temperatures will be a few degrees cooler than Sunday, with treeline temperatures between -5 and -10 C. No new snow is expected. Things continue to cool down and clear up on Tuesday.

Snowpack Summary

10-20 cm of new snow with strong W winds have formed new touchy wind slabs at ridge tops and in open alpine areas. The Nov 8 crust is down 20-30 cm and is present up to ~2400 m. The lower snowpack is a mix of facets and the Oct crusts. Snowpack depths at treeline range from 60-90 cm with up to 140 cm in lee areas.

Avalanche Summary

Sunday had numerous natural, skier triggered and explosive triggered small wind slabs up to size 2. These mostly occurred in lee areas near ridge tops and in the high alpine, though one was observed running to below treeline on the Pilsner Pillar ice climb. Triggering these will remain likely into Monday.

Confidence

Wind effect is extremely variable

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.