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Avalanche Forecast

Archived

Dec 23rd, 2018–Dec 24th, 2018

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 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.

Regions

South Rockies.

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 / southwest to west winds, 20-40 km/h / alpine low temperature near -8°c. MONDAY - Cloudy with sunny periods / light west 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 / light southwest winds / alpine high temperature near -10°c, low temperature near -12°c.

Avalanche Summary

Several explosives triggered avalanches to size 2.5 were reported in the region on Saturday. No new natural avalanches have been reported. One natural size 2 avalanche that was triggered by a cornice was reported in the region on Friday. One size 1.5 explosives triggered avalanche was reported on Thursday.

Snowpack Summary

60-90 cm of recent snow has formed a slab that sits on a persistent weak layer of facets (sugary snow) that formed during the dry weather in early December. Though avalanche activity on this layer has slowed down in recent days, it may still be easy for humans to trigger avalanches on this layer in certain terrain features. Steep features where the underlying ground cover is smooth, places where the snowpack depths are variable, and large convex features are some of the more likely places to trigger this layer. The lower snowpack has a weak structure composed primarily of facets. It is likely that an avalanche triggered on the persistent slab would step down to the lower facets, resulting in a full depth avalanche.

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.