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Avalanche Forecast

Archived

Feb 20th, 2021–Feb 21st, 2021

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

Regions

Banff Yoho Kootenay.

A significant storm will arrive Sunday. Expect conditions to change during the day. By Monday, a significant step back in terrain choice will be warranted.

Weather Forecast

Continued light snowfall overnight Saturday. Sunday, trace amounts of snow, up to 10 cm,  favouring the North part of the region will fall,  as a warm front arrives late in the day. Freezing levels will approach 1800m and alpine winds will reach 70-80km/h. A cold front Monday will bring 10-15cm of snow, peak winds and cooling as it sweeps N to S.

Snowpack Summary

Extensive wind effect with a few thin wind-slabs and fresh cornice growth developing in the alpine. At treeline and below the snowpack is well settled except the surface snow which is facetted and sluffs in steep terrain although wind effect is starting to creep down. A facet and sun crust layer buried Jan 27 persists at treeline down 30-40 cm.

Avalanche Summary

Moderate wind transport at ridge top led to a least one small cornice triggered avalanche in Kootenay NP  today. Sunshine Village reported working with fresh cornice growth and small fresh wind slabs at ridge crests and into  isolated treeline areas. Thursday, Sunshine triggered a very large cornice that initiated a size 2.5 persistent slab.

Confidence

Intensity of incoming weather systems is uncertain 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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.