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Avalanche Forecast

Archived

Dec 23rd, 2016–Dec 24th, 2016

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

Regions

Little Yoho.

We now have a more typical rockies snowpack with firm slabs sitting over a variety of very weak layers. It will be tricky to assess this persistent slab problem. Step way back and limit your exposure to avalanche terrain at tree line and above.

Weather Forecast

Light winds with a SE flow for the weekend and some light snow in Eastern regions. Alpine temperatures will be in the -14C range. A Westerly flow reasserts itself on Monday with some light precipitation and moderate winds.

Snowpack Summary

An average of 15-40cm sits over the weak Dec.19th facets. Wind slabs up to 60cm have been observed over this same layer in alpine areas. The wind slab/facet interface was touchy in avalanche control work over the last 2 days and will persist for some time. The Nov crust is down 30-80cm and as yet there are limited observations of it being reactive.

Avalanche Summary

Explosive control on Wed/Thurs resulted in avalanches up to size 2.5-3 where wind effect was prevalent. The slabs failed on the persistent Dec.19th facets. Ski hills had a couple of size 2 explosive triggered avalanches on the Nov 12 crust on solar aspects with a thin snowpack where the crust is more pronounced. Not many naturals reported or seen.

Confidence

Due to the number and quality of field observations

Problems

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.