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Avalanche Forecast

Archived

Nov 21st, 2020–Nov 22nd, 2020

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

Regions

Little Yoho.

The winds continue to move snow in the alpine so we have kept the hazard elevated for one more day. Areas with less wind effect will have a lower hazard. Keep an eye on the Nov crust layer, the warmer temps on Sunday and early season hazards.

Weather Forecast

A slight clearing trend continues on Sunday with a mix of sun and cloud. Upper winds remain in the moderate to strong range switching from the W and SW. Treeline temperatures will be between -10 and -5 C, with a slight inversion forecast in the alpine with temperatures between -8 and -5 C.

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

One new cornice triggered size 1.5-2 avalanche was observed at Bow Summit Saturday. Local ski areas were again able to trigger new wind slabs in the alpine up to size 1.5 and one size 2 cornice, with ski cutting and explosives. On Thursday a skier remote was reported at 2000m near Watermelon Peak size 1.5 on facets to ground, 40cm deep x 80m wide.

Confidence

Due to the quality of field observations

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.

Loose Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.