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Avalanche Forecast

Archived

Dec 16th, 2012–Dec 17th, 2012

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

Regions

Purcells.

Confidence

Fair - Forecast snowfall amounts are uncertain on Monday

Weather Forecast

Overnight and Monday: A Low pressure system moving along the U.S. border will push some precipitation up into the region. Expect 5-10 mm of precipitation falling as snow at all elevations by Monday morning. Strong SW winds during the storm should become strong NW winds after it passes to the East. Alpine Temperatures should be -7.0 during the day.Tuesday: Dry and cool with Alpine temperatures down to about -13.0 combined with strong NW winds.Wednesday:Continued dry and cool, temperatures dropping down to -16.0 in the Alpine. The next Pacific system is forecast to move in from the coast during the evening.

Avalanche Summary

No new avalanches have been reported.

Snowpack Summary

Thin windslabs have developed in the alpine and at treeline in exposed terrain. Some loose snow sluffing may be experienced in steep terrain. Snow pit test results continue to show weak layers of surface hoar that were buried during mid and late November, however we have not seen any activity on these layers recently. The early season rain crust is another layer that continues to show results in tests, but has not been active. Forecast new snow and strong SW winds are expected to continue to develop wind slabs in the alpine and at treeline.

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.