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Avalanche Forecast

Archived

Feb 28th, 2014–Mar 1st, 2014

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 Inland.

The February weak layer continues to be a concern for triggering a very large avalanche. See the Forecaster Blog for more information.

Confidence

Fair - Wind effect is extremely variable

Weather Forecast

Overnight and Saturday: Mostly clear and cold overnight with strong Northeast winds and very strong outflow winds. Freezing level at valley bottoms and alpine temperatures near -17 overnight. Continued cold and clear with strong Northeast winds and very strong outflow winds.Sunday: Cloudy and cold with a chance of flurries or light snow. Alpine temperatures around -20 combined with strong Northeast winds.Monday: Cloudy and cold in the morning with a chance of sun in the afternoon. Alpine temperatures near -25 with strong Northerly winds.

Avalanche Summary

No new avalanche activity reported.

Snowpack Summary

The recent warm air over most of the forecast regions did not push into the Northwest Inland. Temperatures remained cool even with solar radiation, and now the temperatures have dropped to very cold with the influence of arctic air sliding down from the Northeast. The early February weak layer of facets, crusts, and surface hoar is buried down about 35-90 cm. The snow above the crust has been transported by Southwest winds and then reverse loaded by Easterly or Southeast winds. Cold temperatures have not settled the snow above the weak layer into a cohesive slab, and the cold has preserved the weak layer and associated crusts. I suspect that there will not be much change or improvement in the bonding of the late February snow to the crusts and facets. Snow pack tests may help to show when this layer demonstrates more resistance to added forces.

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.