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Avalanche Forecast

Archived

Jan 17th, 2013–Jan 18th, 2013

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

Regions

South Rockies.

Confidence

Good

Weather Forecast

Friday:  Extreme W ridgetop winds at ridgetop. No precip. Potential above freezing temperatures in the alpine.Saturday:  Strong NW winds at ridgetop. No precip. Potential above freezing temperatures in the alpine.Sunday: Moderate NW winds at ridgetop.  No precip.  Potential above freezing temperatures in the alpine.

Avalanche Summary

No new significant avalanche observations have been reported from the region.

Snowpack Summary

Intense recent winds have redistributed snow and created large cornices. The snow surface is now a mix of sastrugi, hard slab and soft slab in open areas. Below this around 60cm of settled snow rests on a myriad of old surfaces (January 4th interface) that include sun crust on steep south and west facing terrain, surface hoar in sheltered locations at treeline and below and facets everywhere else.  Reports indicate that this bond has strengthened over time and is now fairly tight.  The overlying slab has also settled significantly. The bond at this interface seems to have strengthened somewhat with time. The overlying slab has also settled significantly.

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.