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Avalanche Forecast

Archived

Jan 13th, 2013–Jan 14th, 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 possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
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 - Intensity of incoming weather is uncertain

Weather Forecast

Sunday night and Monday: The ridge of high pressure that has brought cold temperatures lately is being replaced by a warm front pushing in the interior at the end of the day making temperatures warm up significantly, bringing freezing levels unseasonably high and an inversion will keep  the peaks above zero degrees as well. Cloud cover should also dissipate in the alpine with some mid-level clouds. Winds are forecasted to be strong from the Northwest.Tuesday: Similar situation for Tuesday with alpine temperatures being well above normal and strong sun radiation. Winds are expected to be strong from the Southwest.Wednesday:  Temperatures should start cooling in the alpine and a couple disturbances could bring some light precipitation with light Southwest winds.

Avalanche Summary

Numerous glide cracks and a few size 2 avalanches were reported at treeline and below treeline.

Snowpack Summary

The upper snowpack instabilities will most likely become unstable again with the rapid warming that has already started and additional solar radiation on Tuesday. The trigger of a surface instability could step down to the deeper persistent instability creating bigger avalanches. Read the forecaster's blog to learn more about this process. Indeed, the 25 cm of last week's snow is sitting over a weak, faceted old snow surface and a surface hoar layer in some areas. Loose dry sluffing is likely in steep terrain sheltered from the wind. In wind-affected areas, wind slabs have formed behind terrain breaks such as ridges and ribs. A strong mid-pack overlies a weak base layer of facets and the remnants of a crust.

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.