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Avalanche Forecast

Archived

Dec 30th, 2016–Dec 31st, 2016

Alpine
Natural avalanches possible, human triggered probable.
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.

Regions

Lizard-Flathead.

The winds will likely drive the avalanche danger over the next day or so. If you see loose snow drifting or getting blown off ridgecrests, expect an increase in wind slab activity.

Confidence

Moderate - Wind effect is extremely variable

Weather Forecast

Saturday: Mix of sun and cloud with 3-8cm of new snow expected on Saturday night / Moderate westerly winds / Alpine temperatures of -13Sunday: Mix of sun and cloud with light flurries / Moderate northeast winds / Alpine temperatures of -18Monday: Mix of sun and cloud / Strong northeast winds / Alpine temperatures of -20

Avalanche Summary

On Thursday several size 1-1.5 avalanches could be easily ski cut behind ridgecrests on all aspects in the new snow. A few days ago, a large human-triggered avalanche was reported near Corbin in the Flathead Range in an area where wind had firmed up the surface snow and where sugary facets were present lower down in the snowpack. There's lots of loose snow available for redistribution, so if the wind picks up, expect an increase in wind slab avalanche activity.

Snowpack Summary

Up to 50 cm of low density snow has recently fallen, which is now available to be redistributed by mostly moderate westerly winds. The new snow sits above a variety of surfaces including old hard wind slabs and surface hoar. The cold weather in early December left several layers of weak surface hoar and facets which are now buried 50-80 cm deep. These layers are expected to be more in reactive in areas where the overlying slab has gained cohesion with wind or settlement. A thick crust rain crust from mid-November is near the bottom of the snowpack and remains well bonded to the surrounding snow.

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.