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Avalanche Forecast

Archived

Jan 14th, 2013–Jan 15th, 2013

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

Confidence

Poor - Timing, track, or intensity of incoming weather is uncertain

Weather Forecast

Monday night and Tuesday: A high pressure dominates the weather bringing clear skies in the alpine and valley clouds because of the inversion. Alpine temperatures should rise above or near near zero degrees and winds are forecasted to be strong from the West. Wednesday: The high pressure weakens allowing light precipitation. Freezing levels will be around 700 m. and moderate winds from the West.Thursday: Similar conditions expected with slightly more precipitation forecasted, strong West winds and warm temperatures.

Avalanche Summary

A few recent natural slab avalanches up to size 2 and a skier triggered avalanche size 1.5 were reported. The failure plane was the late December surface hoar.

Snowpack Summary

The surface hoar layer down 60-80 cm has started to be reactive in some areas with the warming.  There is also signs of intense wind effect in the alpine by recent strong NW winds leaving shallow areas and hard windslabs on lee side of ridges. The continuing warming and solar radiation forecasted for tomorrow will maintain the weakening of the snowpack trend. Read the forecaster's blog to learn more about this process. Triggering a surface instability could step down to the deeper persistent instability creating bigger avalanches. A strong mid-pack overlies a weak base layer of facets and the early November crust. Even though the crust has been unreactive for a while, professionals are concerned about it again with the warming which could awake it, especially in shallow areas at treeline and in the alpine.

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.