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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

Cariboos.

Confidence

Good

Weather Forecast

Synopsis: A series of frontal systems is expected to affect the region over the next few days bringing steady moderate precipitation and seasonal temperatures.  Thursday: Light to moderate snowfall – 5-10 cm. Winds are moderate and gusty from the west-southwest. The freezing level is around 900 m. Friday: Moderate to locally heavy snowfall – 20-30 cm. Winds are strong from the southwest and the freezing level is around 700 m. Saturday: Cloudy with flurries or light snow. The freezing level is steady at 700 m and winds ease to light from the northwest.

Avalanche Summary

A new size 2.5 natural avalanche was reported on the east side of the region. This event occurred on a south aspect in the alpine and likely failed on a sun crust, down approximately 40 cm.

Snowpack Summary

Variable amounts of new snow continue to add to the recent storm slab which sits above the February 12th weak surface hoar layer and a sun crust on solar aspects. This layer is now buried down about 30-60 cm deep depending on where you are in the region. New wind slabs developed at treeline and above due to the new snow and wind during the storm. These soft new wind slabs (hard slabs in some areas) are reported to be reactive and may be hiding stiffer wind slabs that are a couple of days older. Deeper persistent weak layers from early February and late January continue to show planar failures when moderate to hard forces are applied in snow pack tests. These deeper layers have not been reactive to the weight of a rider, but they may be triggered by large loads like an avalanche in motion, or a cornice fall.

Problems

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.