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Avalanche Forecast

Archived

Feb 20th, 2013–Feb 21st, 2013

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

South Columbia.

Confidence

Fair - Intensity of incoming weather is uncertain on Friday

Weather Forecast

Thursday: Light snowfall intensifying in the evening / Moderate southwest winds / Freezing level at 900mFriday: Heavy snowfall / Strong southwest winds / Freezing level at 1000mSaturday: Light snowfall / Moderate northwest winds / Freezing level at 700m

Avalanche Summary

Recent explosives control produced slab avalanches to size 2.5. The avalanches occurred on a variety of aspects at treeline and in the alpine and are suspected to have ruin on the February 12th interface. A recent natural cornice fall also pulled out a size 2 slab on the slope below.

Snowpack Summary

Variable amounts of low density snow add to the recent storm slab that is between 20-50 cms across the region. These light accumulations may overlie wind slabs which formed a few days ago in the alpine and at treeline. The recent storm slab is expected to remain reactive where it is sitting on the weak surface hoar layer that was buried on February 12th. The recent storm slab has also been reactive on Southerly aspects where a sun crust formed during the period from February 8th-11th. Future loading on the recent storm may cause another cycle of natural activity, or an increased sensitivity to human triggers. There are older weak layers 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.

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.

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.