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Avalanche Forecast

Archived

Dec 26th, 2018–Dec 27th, 2018

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, human triggered possible.

Regions

Lizard-Flathead.

Persistent slabs are tricky to manage. Avalanche activity is receding, but if triggered, an avalanche falling on the persistent weak layer could have serious consequences. Read the latest Forecaster Blog on the persistent slab problem here.

Confidence

Moderate -

Weather Forecast

WEDNESDAY NIGHT: Cloudy with isolated flurries, trace accumulation. Light southwest wind. Alpine high of -9C.THURSDAY: Mix of sun and cloud. Light northwest wind. Alpine high of -9C.FRIDAY: Mainly cloudy with isolated flurries, trace accumulation. Light to moderate west-southwest wind. Alpine high of -11C.SATURDAY: Cloudy with scattered flurries, accumulation up to 5 cm. Moderate southwest wind. Freezing level rising to 1500 m.

Avalanche Summary

Over the weekend, explosives triggered avalanches to size 2.5 and natural avalanches to size 2 were reported. On Sunday, wind redistributing new snow resulted in numerous natural wind slabs avalanches (size 1) noted in the region.

Snowpack Summary

Up to 20 cm of fresh snow is being redistributed into soft wind slabs in lee areas at treeline and alpine elevations. A combined total of 60-110 cm of recent snow has formed a slab that sits on a persistent weak layer that formed in early December. This layer mostly consists of facets (sugary snow) with some isolated areas also containing small surface hoar (feathery crystals). Several other weak layers have been observed in the lower snowpack such as crusts and facets that formed in late October/early November. The potential may exist for avalanches triggered on the persistent slab to step down to these lower layers, resulting in large, destructive avalanches.

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.