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Avalanche Forecast

Archived

Dec 20th, 2015–Dec 21st, 2015

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

Regions

Glacier.

Watch for fresh windloading and storm slab development on lee slope terrain features.

Weather Forecast

10cm of storm snow expected today accompanied by moderate SW winds.  Another 5cm is forecast to fall tonight through tomorrow. 

Snowpack Summary

20cm+ of low density storm snow have fallen over the last 72hrs with another 10cm expected today.  A large amount of snow is available for wind transport with moderate SW winds expected to kick in mid morning today.  80cm+ settled snow sits on top of the Dec 2nd interface which consists of SH below treeline and suncrust on steep solar aspects.

Avalanche Summary

Six size 2-2.5 slab avalanches observed out of steep N facing terrain just east of Rogers Pass.  These slabs initiated in the storm snow.

Confidence

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

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.