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Avalanche Forecast

Archived

Dec 21st, 2011–Dec 23rd, 2011

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 and human triggered avalanches likely.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.

Regions

Northwest Coastal.

Confidence

Good - -1

Weather Forecast

Thursday: Ridgetop winds 100-115km/hr. Snow amounts up to 30cms during the day. Freezing levels may rise to 800m. Friday-Saturday:Ridgetop winds SW 60-75km/hr. Snow amounts up to 35cms. Freezing levels may rise to 1100m then drop to valley bottom by Sunday.Snowfall amounts will be lower in the Southern parts of the region.

Avalanche Summary

A widespread natural avalanche cycle hit the region on Tuesday. Large natural and explosive controlled avalanches up to size 3 occurred on all aspects at all elevations. A natural size 4 also occurred on a SE aspect around 1600m.We may see another widespread avalanche cycle Thursday and Friday. Once it stops snowing and blowing the new snow should start to settle out, and avalanche danger will decrease.

Snowpack Summary

The forecast region got slammed by snow, wind and fluctuating freezing levels. The southern part of the region has received up to 70cms which totals over a meter of new snow over the past week (Kasiks, Terrace areas). Locations to the north are seeing less (Stewart up to 40cms). 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. The storms over the past 10 days have created several significant avalanche cycles. My guess is that these repeated cycles have cleaned out most of the mid-December buried surface hoar/facet interface. This is good. The region now sees firm wind pressed surfaces, old bed surfaces (from previous slides), and a crust that extends up to alpine elevations in the south and around 1000m in the north. The next storm will fall on these surfaces, and it's likely that the region will see another large avalanche cycle. The mid and lower snowpack are settled 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.