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Avalanche Forecast

Archived

Mar 3rd, 2012–Mar 4th, 2012

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
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

Good

Weather Forecast

Sunday: Moderate to heavy snow. Freezing level 500m, rising to 1100-1400m by afternoon. Strong south-westerly winds.Monday: Moderate to heavy snow. Freezing level falling in the afternoon, reaching valley bottom overnight. Light to moderate north-westerly winds.Tuesday: Light snow. Freezing level valley bottom. Light to moderate westerly winds.

Avalanche Summary

Many avalanches have been triggered remotely (from several hundred metres away) and accidentally by skiers and machinery this week. These avalanches were failing on upper snowpack persistent and storm snow weaknesses, on almost all aspects and elevations. Initial reports on Saturday indicate that a natural avalanche cycle has begun, with avalanches running near full-path and failing on a variety of aspects.

Snowpack Summary

Snow is falling with strong winds and fluctuating temperatures, creating a perfect recipe for new storm slab and wind slab instabilities. This new snow is landing on variable surfaces including surface hoar and facets. Widespread persistent weak layers buried in February have remained touchy all week and are a key concern at all elevations. Storm slabs, wind slabs and sluffs could trigger these deeper weaknesses, creating avalanches which are larger than you expect, given the amount of fresh snow. Large cornices also loom as potential triggers for deep avalanches.

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.