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Avalanche Forecast

Archived

Jan 4th, 2014–Jan 5th, 2014

Alpine
Natural and human triggered avalanches likely.
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.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

South Rockies.

Confidence

Good

Weather Forecast

Tonight and Sunday: Arctic air is flowing over the interior regions bringing strong to extreme winds from the NW. These should ease slightly on Sunday. Mainly clear skies and freezing levels at valley bottom.Monday: Moderate to strong NW winds and clear skies. Freezing level is at valley bottom, however, an above freezing layer is expected to warm things up between 1700 m and 2500 m of elevation.Tuesday: A weak front is supposed to arrive from the coast with light precipitation and with cooler air moving in aloft again.

Avalanche Summary

A natural avalanche cycle happened following the storm. Avalanches up to size 2 were observed in the alpine and at treeline on all aspects. An avalanche size 2 would have ripped out in mellow terrain at treeline and is suspected to have run on a deeper facetted layer. More avalanches are suspected tomorrow with the reloading of slopes from wind and snow available for transport.

Snowpack Summary

Strong to extreme NW winds forecasted for tomorrow is why danger rating is staying up again in the alpine tomorrow. Limited winds today have left the storm snow available for transport and reloading of slopes tomorrow. New windslabs could grow quite thick near ridge top and most likely be very touchy. Storm snow is settling but beware of the possibility of sluffing in steep sheltered terrain. Even though avalanche problems are starting to be more specific, I would still show respect to the deeper persistent weak layers that are still showing sudden planar results and have been suspected to be active during the avalanche cycle. For example, a windslabs could trigger a deeper slab avalanche in steep rocky terrain where basal facets and depth hoar exist. The surface hoar layer or crust/facet combo down a 100 cm is the other deep persistent weak layer that is still a concern to avalanche professionals.

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.