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Avalanche Forecast

Archived

Jan 11th, 2017–Jan 12th, 2017

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

Regions

Little Yoho.

Steady winds from the north have blown most of the recent snow into hard slabs in unusual locations (reverse loading).  If winds pick up Thursday ice climbers should be mindful of overhead terrain.  SH

Weather Forecast

Expect alpine temperatures to be in the -15C range on Thursday, with much colder temperatures (-20's) in the valley bottoms.  NW winds will increase in the afternoon.  There is no snow in the 3 day forecast and there will be a gradual warming trend into the weekend.

Snowpack Summary

Up to 20 cm of low density snow has been blown into hard wind slabs from north winds, so expect locally deep pockets of dense wind drifts in unusual areas (reverse loading). These slabs overlie a some facet layers with the main problem being the Dec 19 interface of facets, now buried down about 50-70 cm.

Avalanche Summary

No avalanche activity reported or observed in Little Yoho today, but we have minimal observations from this area - so low confidence.

Confidence

Due to the number of field observations on Wednesday

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.