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Avalanche Forecast

Archived

Feb 16th, 2020–Feb 17th, 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 unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Banff Yoho Kootenay.

Triggering wind slabs continues to be the main concern, however recent wind loading has also caused large sluffs in gullies, several natural cornice failures and failures on the deep persistent layer. Continue to choose terrain with low consequences.

Weather Forecast

Moderate NW alpine winds with light flurries are forecast on Monday with alpine temperatures between -15 and -18 C. Winds become light and shift to the N on Tuesday as a clearing trend occurs. Wednesday is also clear but temperatures will rise to near freezing.

Snowpack Summary

Extensive wind effect in the alpine with wind slabs at ridge tops and in lee areas. Up to 35cm of snow over the last few days sits over a well settled upper and mid-pack. In many areas the lower snowpack consists of weaker facets and depth hoar that are still producing moderate shears in snowpack tests. The Feb 1 crust is present below 1900m.

Avalanche Summary

A few natural cornice failures and wind slab avalanches up to size 2.5 were reported Sunday as well as ski cutting and explosive triggered wind slabs up to size 2 at the local ski areas. On Saturday a skier triggered size 3 was reported on Copper Mountain and an explosive triggered size 3 occurred at Sunshine that both failed on the basal facets.

Confidence

Freezing levels are uncertain on Wednesday

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.