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Avalanche Forecast

Archived

Feb 19th, 2012–Feb 20th, 2012

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

Fair - Timing, track, or intensity of incoming weather is uncertain

Weather Forecast

In general we should see unsettled conditions as a series of disturbances move across the province this week. Monday: Light to locally moderate snowfall - 5-10cm. Freezing level (FL) 800m. Winds light to moderate from the southwest. Tuesday: Light to locally moderate snowfall - 10-15cm. FL rising to 1200m. Winds increasing to moderate from the W-SW. Wednesday: The strongest pulse should arrive late on Tuesday and bring moderate to locally heavy precipitation into Wednesday. 15-30cm is possible. FL lowering to 800-1000m. Winds moderate from the SW.

Avalanche Summary

There is one new report of a Size 1 accidently triggered avalanche on a steep leeward (north) aspect in the alpine. Otherwise there have been no new reports.

Snowpack Summary

The new snow layer above the February 9 surface hoar is now about 15-35cm thick. This surface hoar layer may be widespread in some areas, while others have reported it being confined to shady aspects at treeline and in the alpine. Some thin windslab has developed as a result of SW winds Fri/Sat. A melt-freeze crust has developed on solar aspects at all elevations, and on all aspects below about 1600 metres. The mid-pack is generally well settled. There is some concern that large loads like cornices may trigger the Jan. 20th facet layer. Some shallow snowpack areas may continue to have a weak layer of basal facets near the ground.

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.