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Avalanche Forecast

Archived

Mar 25th, 2013–Mar 26th, 2013

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 unlikely, human triggered possible.
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.

Avalanche danger may spike on slopes that are getting warmed by sunshine or warm temperatures. Be alert for changing conditions throughout the day.

Confidence

Fair - Timing or intensity of solar radiation is uncertain

Weather Forecast

Tuesday-Thursday: No snow. Light to moderate SW winds. Alpine temperatures near -4.

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 near Bear Pass and other areas. On Saturday there was a report of a size 2 avalanche, triggered from a distance by a snowmobile. This slide probably failed on the March 9 surface hoar. Many skier-triggered and skier-remote avalanches of size 1-3.5 were reported last week, with the bulk of events failing on the March 9th surface hoar layer down around 50 cm.

Snowpack Summary

Recent new snow is settling with the influence of warm temperatures. Wind slabs may be found at alpine and treeline elevations. A layer of surface hoar (buried March 9th; now down about 40-60 cm) has been found at all elevations. It’s slowly becoming less touchy, but professionals are keeping a wary eye on it. Triggering this layer is becoming a low probability but high consequence problem. Check out the Forecaster's Blog for related discussion. A second surface hoar layer, buried on March 18, is also reported to be gaining strength. The mid snowpack is generally well settled and strong. Cornices are large and untrustworthy, especially when the sun is out.

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.