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Avalanche Forecast

Archived

Feb 22nd, 2013–Feb 23rd, 2013

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

Regions

Cariboos.

Confidence

Good

Weather Forecast

Synopsis: There is a brief break between weather systems on Saturday before the next frontal system arrives late Sunday and into Monday.  Saturday: Cloudy with light snow in the morning and gradual clearing through the day. The freezing level is near valley bottom and winds ease to moderate from the west-northwest. Sunday: Moderate snow – around 10 cm. The freezing level is near valley bottom and winds are moderate from the west. Monday: Snow easing in the morning with gradual clearing throughout the day. The freezing level remains near valley bottom. 

Avalanche Summary

Avalanche activity on Thursday was primarily limited to loose dry avalanches in steep terrain, indicating that a slab had not yet formed. This has almost certainly changed today. Heavy snow and strong winds on Friday will likely result in a natural avalanche cycle which should continue into the weekend.

Snowpack Summary

By late Friday morning there was already up to 30 cm of new snow on the ground. This new snow was accompanied by strong west-southwest winds forming weak wind slabs in exposed lee terrain. The February 12 persistent weak layer (crust, and/or surface hoar) is now down 60-80 cm and is primed for triggering. Recent snowpack tests have shown easy to moderate "pops" results on this interface. Deeper persistent weak layers from early February and late January continue to show planar failures when moderate to hard forces are applied in snow pack tests. These deeper layers have not been reactive to the weight of a rider, but they may be triggered by large loads like an avalanche in motion (step-down avalanche), or a cornice fall.

Problems

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.