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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

Cariboos.

Confidence

Good

Weather Forecast

Sunday: Moderate to heavy snow. Freezing level 500m, rising to 1000m by afternoon. Strong south-westerly winds.Monday: Moderate snow. Freezing level valley bottom. Light to moderate north-westerly winds.Tuesday: Light snow. Freezing level valley bottom. Light to moderate westerly winds.

Avalanche Summary

As I write this, it's still too early for reports of storm-related avalanche activity, but I expect a natural cycle is well under way. Occurrences throughout the week illustrate the unpredictable nature of persistent weak layers in the upper snowpack. On Thursday, a skier triggered a size 2.5 slab very easily and very close to recent ski tracks, which failed on buried surface hoar. On Wednesday, a cornice fall triggered a size 2 slab on a north aspect, which failed on the Feb 16. weakness. On Tuesday, numerous size 2-3 avalanches ran naturally, or with a remote trigger, on a variety of slopes. Most failed on upper snowpack persistent weaknesses. These layers are touchy and are likely to fail under the new storm load, creating large or widely-propagating avalanches.

Snowpack Summary

Snow is falling with strengthening winds and rising temperatures onto variable surfaces including surface hoar and facets. This is creating a nice recipe for new storm slab and wind slab instabilities. Persistent weak layers buried in February are a key concern at all elevations and could be triggered by storm slabs, wind slabs or sluffs, or with a light additional load (like you). Avalanches may be unexpectedly large, 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.