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Avalanche Forecast

Archived

Dec 21st, 2013–Dec 22nd, 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 possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Glacier.

Weather Forecast

Isolated flurries are forecast today, with freezing levels remaining at valley bottom and light to moderate NW ridge top winds.  A pacific frontal system is forecast to bring light, possibly moderate snow starting tonight and continuing into Monday.  Freezing levels are forecast to rise to 1000m on Monday.

Snowpack Summary

Up to 80cm of snow has settled over surface hoar at lower elevations, mixed forms and variable wind slabs at higher elevations. This interface failing sudden planar in snowpack tests. Strong winds have formed wind slabs and wind loaded pockets at treeline and above. At the base of the snowpack 2 persistent weak layers are surrounded by mixed forms.

Avalanche Summary

Natural avalanche activity has tapered off, but slabs now sit at depths easily triggered by light-loads, like humanoids. A number of field crews in the Pass yesterday backed off of larger slopes due to the ease in which the slabs were reacting down 70-80cm.

Confidence

Intensity of incoming weather systems is uncertain on Monday

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.