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Avalanche Forecast

Archived

Dec 16th, 2018–Dec 17th, 2018

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Purcells.

Have patience with this recent storm snow. It is going to take some time for things to stabilize. The potential for human triggered avalanches remains likely! Choose low angle terrain and avoid overhead hazard.

Confidence

Moderate - Intensity of incoming weather systems is uncertain

Weather Forecast

SUNDAY NIGHT -Flurries, up to 5 cm / south to southwest winds, 25-50 km/h / alpine low temperature near -4MONDAY - Cloudy with flurries, 5-10 cm / southwest winds, 25-50 km/h, gusting to 60 km/h / freezing level 1600 m / alpine high temperature near -5TUESDAY - Snow, 10-20 cm / southwest winds, 20-50 km/h, gusting to 60 km/h / freezing level 1500 m / alpine high temperature near -4, low temperature near -6WEDNESDAY - Mainly cloudy with flurries, up to 10 cm / west to southwest winds, 20-40 km/h, gusting to 60 km/h / freezing level 1500 m / alpine high temperature near -5, low temperature near -8

Avalanche Summary

Avalanche activity has been extensive in the Purcells over the past 5 days with daily reports of natural and explosive triggered avalanches to size 3.5, and human triggered avalanches to size 2.5. Many of these have been remote triggered (triggered from a distance).One very notable report on Saturday was a size 2.5 human triggered avalanche that was remotely triggered from 50-100 m away on a northwest aspect at 2250 m. A report of this avalanche can be found on the Mountain Information Network. (here)A natural avalanche cycle to size 4 was also reported in the region on Friday.

Snowpack Summary

60-120 cm of snow sits on a weak layer of facets (sugary snow), surface hoar (feathery crystals), and a sun crust (on south facing slopes). Strong winds have promoted widespread slab formation.Another layer of surface hoar and sun crust is now buried 80-150 cm. The potential may exist for smaller avalanches to step down to this deeper layer, resulting in very large avalanches. The most likely areas for this layer to be a problem is where the surface hoar sits on the sun crust, which is most likely on steep south facing terrain at treeline.At the base of the snowpack is a crust that formed in late October. This layer is likely only a problem on large, steep alpine features with a shallow snowpack. It would likely take a large trigger, such as a cornice fall, to produce an avalanche on this layer.

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.