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Avalanche Forecast

Archived

Dec 23rd, 2011–Dec 24th, 2011

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

Regions

Northwest Coastal.

Confidence

Fair - Intensity of incoming weather is uncertainfor the entire period

Weather Forecast

Saturday: 20-30cm of snow - moderate to strong southwest winds - freezing level at 1000mSunday: 8-15cm of snow - moderate southwest winds - freezing level at surfaceMonday: moderate snowfall - Moderate winds from the south - freezing level at surface

Avalanche Summary

Limited observations at this time. Expect widespread natural avalanche activity throughout the weekend for forecast wind and snow.

Snowpack Summary

Earlier this week the forecast region got slammed by snow, wind and fluctuating freezing levels. Including the 20cm that fell on thursday night, the southern part of the region has received over a meter of new snow over the past week (Kasiks, Terrace areas). Locations to the north are seeing less (Stewart up to 60cms). This new snow has been blown around by extreme-strong southwest winds creating stiff wind slabs on lee slopes. The winds have switched from the SW to the NW. This switch was short lived through Wednesday, but may have formed new wind slabs on SE - S facing slopes. This makes the wind slab problem even trickier to predict. In addition to the more obvious direct-action storm instabilities that are expected with the forecast weather, local avalanche professionals have some other concerns: Surface hoar that formed during the winter solstice sits approximately 30cm below the surface and will become more reactive with more wind and snow. As well, the crust-facet combo (extends up to alpine elevations in the south and around 1000m in the north) from the early december dry-spell sits about 135cm below the surface and has not gone away . Any avalanches on this layer would be highly destructive and is probably waiting for the right load or trigger. The mid and lower snowpack are settled out and strong. Snowpack depths in the Kasiks, Terrace areas are reaching the 300cm mark. Further north Smithers, Bear Pass depths are ranging from 180-250cms.

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.

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.

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.