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Avalanche Forecast

Archived

Dec 15th, 2014–Dec 16th, 2014

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

Regions

South Rockies.

Danger ratings trending down due to low freezing levels after the recent rain.

Confidence

Fair - Due to the number of field observations

Weather Forecast

Mainly sunny and dry for the forecast period. Freezing levels will remain in valley bottoms with alpine temperatures reaching -5C and light to moderate westerly alpine winds.

Avalanche Summary

No new reports of avalanches from the region on Sunday or Monday morning.

Snowpack Summary

Surface hoar is likely growing on a thick hard supportive near-surface rain crust that extends as high as 2100 m, with as much as 15cm of fresh snow on it. Last week's rain and subsequent freezing temperatures has effectively stabilized the snowpack at all but the highest elevations. However, in high alpine areas that did not get rain during the recent storm, there may be a buried persistent weak layer of crust and/or facets that is now down between 70-100 cm. This buried crust from November may continue to be triggered by large additional loads. Pockets of fresh wind slab may also be triggered at or near ridgetops in areas where the snow was dry enough to be transported by the strong Southwest winds during the storm.

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.