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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 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.

Regions

South Columbia.

Confidence

Fair - Intensity of incoming weather is uncertain for the entire period

Weather Forecast

Saturday: Light to locally moderate snowfall / Moderate northwest winds (with strong gusts) / Freezing level at 700mSunday: Light to locally moderate snowfall / Moderate to strong west winds / Freezing level at 900mMonday: Light snowfall / Light southwest winds / Freezing level at 1000m

Avalanche Summary

Observations from the region have been very limited due to poor visibility; however, there have been reports of widespread avalanche activity occurring within the recent storm snow. I expect widespread avalanche activity to continue throughout the weekend with the potential for very large avalanches.

Snowpack Summary

Moderate to locally heavy snowfall and wind have created potent new storm slabs which are most reactive in wind-exposed terrain. These new accumulations are adding to the 25 to 55cm of snow which overlie the weak surface hoar layer which was buried on February 12th. The additional weight of the new snow and wind affect is expected to add reactivity to this persistent weakness which remains a primary concern for professionals in the region. This interface has also shown reactivity on south aspects where a sun crust also exists. There are older weak layers (surface hoar, crusts on solar aspects, facets) that are now buried down around 60-80 cms and also at about 110 cms. These layers have been unlikely to trigger by skiers, but they may still be sensitive to large loads like avalanches in motion or 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.