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Avalanche Forecast

Archived

Mar 9th, 2013–Mar 10th, 2013

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

Regions

Purcells.

Confidence

Fair - Track of incoming weather is uncertain

Weather Forecast

Saturday night and Sunday: Winds will pick up as the next system is moving in but precipitation will not be as much as forecasted yesterday. Expect just light precipitation starting late during the day with moderate to strong winds from the W.  Freezing levels should still rise to 1300 m. but solar radiation will be much less than Saturday.Monday:  Trace precipitation amounts (light amounts over the S part of the region) are expected with mostly cloudy skies, moderate W winds and slightly cooler temperatures and lower freezing levels. Tuesday: Timing and track of the next system is still uncertain, but there is a potential for a fairly active system that could deliver interesting amounts of precipitation.

Avalanche Summary

3 natural slab avalanches size 3 were reported that would have been triggered by solar radiation on S and SE aspects. Smaller loose wet and dry avalanches were reported out of steep terrain on all aspects. There was also an observation of a large cornice failure on a N aspect which did not trigger a slab on the slope below.

Snowpack Summary

New windslabs are expected to form on lee features of forecasted moderate W winds in the alpine and below ridgetops at treeline. Older windslabs also exist in the alpine which were formed by the N winds yesterday. These will be susceptible to sledder and skier triggering. The deeper surface hoar/sun crust persistent weak layer down 60-90 cm is less reactive to skier traffic but could still be triggered by a large load (like a cornice fall or a windslab avalanche stepping down). This layer remains a concern to professionals. At the surface of the snow, expect to find a suncrust on SE-S-SW facing slopes at all elevations (especially on steep slopes), a melt-freeze crust all the way up to 1600 m. and possibly some surface hoar on shaded slopes above that elevation.

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.