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Avalanche Forecast

Archived

Mar 23rd, 2013–Mar 24th, 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 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 unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Northwest Coastal.

Confidence

Fair - Due to variable snowpack conditions

Weather Forecast

Sunday: Cloud building during the day. Light snow, starting late in the day. Light winds. Alpine temperature near -4.Monday: Light snow. Moderate S winds. Alpine temperature near -4.Tuesday: No snow. Light winds. Alpine temperature near -5.

Avalanche Summary

Naturally-triggered wind slabs and loose moist avalanches have been observed over the last couple of days. Ice fall also triggered size 2.5-3 avalanches in the north of the region.Many skier-triggered and skier-remote avalanches of size 1-2.5 were reported last week, with the bulk of events failing on the March 9th surface hoar layer down around 50 cm. Numerous other skier-remote (from up to 800 m away) avalanches of size 2-2.5 also failed just to the NE of the forecast region, on the same layer. A very large (size 3.5) avalanche was triggered in Cherry Bowl in the Shames backcountry on Sunday. Click here for a full report.

Snowpack Summary

Recent new snow overlies surface hoar, crusts and old wind slabs. New wind slabs have formed lee to SW to NW winds. The surface hoar (buried March 9th; now down about 40-60 cm) has been found at all elevations. Its reactivity (initially electric) is becoming more variable. Remote-triggering of avalanches last week indicated the volatility of this layer. A slow improvement is occurring, but confidence is not soaring amongst professionals, who continue to tread carefully by making conservative terrain choices. Triggering this layer is transitioning into a ‘low probability/ high consequence” phase. Check out the Forecaster's Blog for tips on how to deal with this type of problem. A second surface hoar layer, buried on March 18, is also problematic in some areas. The mid snowpack is generally well settled and strong. Cornices are large and untrustworthy, especially when the sun is out.

Problems

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.

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.