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Avalanche Forecast

Archived

Feb 26th, 2012–Feb 27th, 2012

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

Regions

South Columbia.

Local areas receiving direct sunshine may spike to HIGH danger.

Confidence

Good

Weather Forecast

Monday: Mainly clear and sunny, with valley cloud. No precipitation. Light westerly winds. Freezing level valley floor. Tuesday/Wednesday: Flurries possible on western slopes. Light-moderate south-westerly winds. Becoming slightly milder.

Avalanche Summary

Many large natural and human-triggered avalanches have been reported each day since Wednesday. Natural activity (up to size 3.5) spiked following the heaviest snowfalls on Tuesday night and Friday night. Skiers have been triggering avalanches (mostly size 1-2.5) accidentally and remotely. These are running on storm snow instabilities or persistent weaknesses in the upper snowpack. There have been some lucky escapes. Conditions will remain ripe for human-triggering after the more obvious signs of instability (like new snowfall, wind-loading and natural activity) die down.

Snowpack Summary

Deep wind slabs exist on many aspects at all elevations. Storm snow totals range from about 60-140cm above the Feb 16. surface hoar layer and the Feb. 8 interface. The Feb. 8 interface is a combination of weak layers: in most locations it marks a widespread surface hoar layer. On steep south- and west -facing aspects, a sun crust that formed during the drought was also buried on Feb. 8th. This crust probably has a bit of faceting below it too, meaning that most terrain in the region has a weak layer in the upper snowpack. Recent remote and natural triggering indicates the touchy nature of these weaknesses. Large cornices threaten many slopes.

Problems

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.

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.