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Avalanche Forecast

Archived

Dec 22nd, 2017–Dec 23rd, 2017

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.
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.

Deep powder offers excellent riding in many areas, but there's a highly variable weak layer that warrants cautious terrain choices. Read this forecasters' blog for more details.

Confidence

Moderate - Wind effect is extremely variable

Weather Forecast

SATURDAY: Dry and sunny, moderate northwest winds, temperatures around -15 C.SUNDAY: Sunny with increasing clouds, light northwest winds, temperatures around -15 C.MONDAY: Mix of sun and cloud, light northwest winds, temperatures around -18 C.

Avalanche Summary

A natural avalanche cycle was observed in alpine terrain on Friday with storm slabs up to size 2 (typically 20-40 cm deep). Explosive avalanche control triggered similar sized avalanches.

Snowpack Summary

Around 50 to 80 cm recent new snow now rests on a variety of old surfaces. These old surfaces include crusts on south through west facing slopes, wind-scoured slopes and, in sheltered terrain at and below treeline, large feathery surface hoar crystals. Lower in the snowpack, you should be able to find a hard crust that was buried near the end of November. This crust is approximately 30 cm thick and extends from 1600 m to mountain top on all aspects. Average snowpack depths at treeline in the region range from 100 to 140 cm.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

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.