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Avalanche Forecast

Archived

Dec 23rd, 2018–Dec 24th, 2018

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 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

Lizard-Flathead.

Persistent slabs are tricky to manage and generally require patience and conservative terrain choices. Check out the new Forecaster Blog for a great explanation on how to best manage a persistent slab problem. Click here to read the blog.

Confidence

Moderate - Due to the number of field observations.

Weather Forecast

SUNDAY NIGHT - Cloudy with clear periods and isolated flurries, up to 5 cm / southwest to west winds, 20-40 km/h / alpine low temperature near -6°c. MONDAY - Cloudy with sunny periods / light southwest winds / alpine high temperature near -8°c. TUESDAY - A mix of sun and cloud / light southwest winds / alpine high temperature near -8°c, low temperature near -10°c. WEDNESDAY - Cloudy with sunny periods and isolated flurries / light southwest winds / alpine high temperature near -9°c, low temperature near -11°c.

Avalanche Summary

Several explosives triggered avalanches size 1-2.5 were reported in the region on Saturday. No new natural avalanches were reported on Saturday.Several natural and explosives triggered avalanches to size 2 were reported on Friday.

Snowpack Summary

10 cm of snow fell during the day on Sunday. This new snow has been redistributed into soft wind slabs in lee areas at treeline and alpine elevations. 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.