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Avalanche Forecast

Archived

Dec 11th, 2013–Dec 12th, 2013

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

Regions

Purcells.

If you receive more then 15 cm of new snow in your local riding area, consider the danger ratings to be one step HIGHER.

Confidence

Fair - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

Interior regions will start to see light-moderate amounts of snow, gradual warming and strong ridgetop winds as the weakening cold front passes through on Thursday. The Northern part of the Purcells may see fewer accumulations.Thursday: Cloudy. Snow amounts 10-15 cm. Alpine temperatures near -9. Ridgetop winds moderate from the West.Friday: Precipitation will taper off as we see a break in the system. Cloudy skies, snow amounts near 5 cm. Alpine temperatures -9. Ridgetop winds strong from the West.Saturday: Cloudy with snow amounts near 5 cm. Alpine temperatures -7. Ridgetop winds moderate from the SW.

Avalanche Summary

Wind slab avalanches up to size 1.5 have been easily triggered under the weight of a rider, most commonly on N-NE aspects, cross-loaded features and the immediate leeward side of ridge crests. Loose dry surface sluffing from steeper terrain is expected, use caution near terrain traps like cliffs, and depressions.

Snowpack Summary

Shifting winds have formed stiff wind slabs on the lee side of ridge lines. Snowpack depths at treeline vary across the region, averaging 70-110 cm. Widespread surface hoar development and surface faceting exists from the previous cold temperatures and is now getting buried by incremental snowfall amounts. In the Southern part of the region there is 40-70cm of low density snow over the late-November surface hoar/ crust/ facet interface. This layer may become reactive as it sees additional load, and warming temperatures, forming more of a slab.In the Northern part of the region the lower/mid snowpack is weak, composed of an early season crust (more prevalent on north aspects) weak faceted crystals and depth hoar above and below the crust. This persistent slab may be stubborn to trigger, but if triggered have high consequences.

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.