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Avalanche Forecast

Archived

Jan 17th, 2017–Jan 18th, 2017

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 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, human triggered possible.

Regions

Purcells.

There is a lot of uncertainty surrounding the intensity of precipitation amounts in the region. Certainly in areas where the freezing level is forecast to rise in combination with the potential for snowfall, the avalanche danger will be elevated.

Confidence

Moderate - Intensity of incoming weather systems is uncertain on Wednesday

Weather Forecast

WEDNESDAY: Flurries with 10-20 cm of accumulation, moderate south winds, freezing level rising to around 1500 m throughout the region.THURSDAY: Cloudy with isolated flurries, light to moderate southwest winds, freezing level around 1500m.FRIDAY: Cloudy with sunny periods, light southwest wind and freezing level 1300m.More details can be found on the Mountain Weather Forecast.

Avalanche Summary

Expect new snow and wind to build fresh and touchy wind slabs. Warming and and increased loading will also give a rise to the likelihood of triggering persistent slab avalanches.

Snowpack Summary

Expect 10-20 cm of new snow Tuesday night into Wednesday with greater accumulations in the southern part of the region. The new snow, wind, and warming will build touchy storm slabs that will be extra thick and reactive on wind-loaded features. In sheltered areas, the new snow is burying a layer of feathery surface hoar that may produce surprisingly wide propagations. The main concern deeper in the snowpack is a layer of sugary facets from mid-December that can be found between 50 and 100 cm deep. This layer was considered dormant during the recent cold weather, but may become reactive as warm temperatures soften the overlying slab.

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.