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Avalanche Forecast

Archived

Feb 24th, 2012–Feb 25th, 2012

Alpine
Natural and human triggered avalanches likely.
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 possible, human triggered probable.

Regions

South Coast.

Confidence

Good

Weather Forecast

Saturday: Expect snowfalls to taper under northwesterly winds. As winds shift to northeasterly late in the day we could see some convective flurries. Temperatures could reach -9. Sunday & Monday: Expect a clearing trend, with light northerly winds and temperatures reaching -8 in the afternoon.

Avalanche Summary

Natural avalanches up to size 3.0 and ridder triggered up to size 1.5 has been observed. these have been predominantly on north through east aspects at treeline and in the lower alpine.

Snowpack Summary

Over the past week up to 40 cm of new snow fell over the Duffey Lake area, this snow fell incrementally and low density. The Coquihalla has seen up to 50 cm. This new snow has buried a variety of old snow surfaces. The old surfaces include: melt-freeze crusts on all aspects below 1700m and on steep solar aspects higher up, surface hoar (feather like crystals), old wind slabs, and facets (sugary crystals), which exist on north aspects as well as around crusts. I suspect these buried weak layers will become naturally reactive with forecast snow and wind, and the slopes that don't slide naturally may be ripe, waiting for a rider trigger. Below this sits a well settled snowpack, with treeline snowpack depths near 250cm. Test results on the Duffey yesterday shows RB5 - whole block down 22cm, sudden planar results. The warning signs are clear and a large avalanche cycle has started in the interior regions. Please visit our Forecaster's Blog for more detailed information. To view recent photos of this buried surface hoar in the Coquihalla area please check out this link: https://avalanche.ca/cac/library/avalanche-image-galleries/avalanches2012

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.