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Avalanche Forecast

Archived

Dec 27th, 2018–Dec 28th, 2018

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

South Rockies.

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

Low - Due to the number of field observations

Weather Forecast

THURSDAY NIGHT: Cloudy with clear periods. Light northwest wind. Alpine low -13C.FRIDAY: Mix of sun and cloud. Light increasing to moderate west wind. Alpine high of -11C.SATURDAY: Cloudy with scattered flurries, trace to 10 cm accumulation. Moderate west wind. Freezing level rising above 1200 m.SUNDAY: Mix of sun and cloud. Light northwest wind with occasional moderate-strong gusts. Alpine high -8C.

Avalanche Summary

The persistent weak layer was active last weekend, explosives triggered avalanches to size 2.5 and a cornice triggered a size 2 avalanche. Skier traffic was also able to trigger wind slab avalanches to size 2. Information in this region is limited. Post your observations to the Mountain Information Network here.

Snowpack Summary

Winds have redistributed snow in the alpine and treeline, stripping areas exposed to the wind and creating hard wind slabs in wind-loaded terrain. In total, 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 over a crust on the ground. It is very 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.