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Avalanche Forecast

Archived

Feb 23rd, 2013–Feb 24th, 2013

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
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 - Timing, track, or intensity of incoming weather is uncertain on Sunday

Weather Forecast

Sunday: Heavy snowfall developing late in the day and continuing overnight / Strong west winds / Freezing level at 900mMonday: Light snowfall / Light northwest winds / Freezing level at 800mTuesday: Mix of sun and cloud / Light southwest winds / Freezing level at 800m

Avalanche Summary

A size 2 slab avalanche occurred on Friday in the north of the region and resulted in a fatality. The avalanche occurred on a northeast aspect at treeline, More details will follow as they are released by the RCMP.

Snowpack Summary

Up to 50cm of new snow and wind have created potent new storm slabs which are likely to be most reactive in wind-exposed terrain. These heavy accumulations add 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 southerly aspects where a sun crust formed during the period from February 8th-11th. 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.