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Avalanche Forecast

Archived

Mar 11th, 2017–Mar 12th, 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 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

Little Yoho.

Danger ratings over the next few days will be determined by how warm it gets in Little Yoho. Watch for exposure to cornices, and dig down to see how the storm snow/deeper weak layers are reacting. 

Weather Forecast

Valley bottom temperatures will go above 0C Sunday, with alpine temperatures staying in -8 to -10C range with moderate W alpine winds and a few cm of snow each day through the early part of next week.

Snowpack Summary

60-70cm of storm snow this week has been reactive but is settling with the warmer temperatures. Winds at upper elevations have formed variable wind slabs and cornices, the latter being touchy Saturday.  Persistent weak layers in the midpack have been gaining strength and are becoming less of a problem, especially in deeper areas close to the Wapta. 

Avalanche Summary

We have had many large, deep avalanches this week, both natural and along highway control paths. Less activity was noted Saturday except for widespread cornice failures which were formed this past week.

Confidence

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

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.