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Avalanche Forecast

Archived

Dec 21st, 2020–Dec 22nd, 2020

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Glacier.

One more storm before Santa gets a weather window to deliver powder faceshots.

With the arrival of the afternoon storm, danger levels will bump up as a natural avalanche cycle rips through the area.

Perhaps it's best to go sample your ski hill today!

Weather Forecast

A storm tracking along the international border will spin some snow and reverse (N and E) winds our way.

Today: Snow starting near noon, 10-15cm, mod E winds, FZL 1000m

Tonight: Snow,10cm, FZL at valley bottom, mod N ridge-top winds.

Tues: Cloudy with sunny periods, nil snow, FZL 500m, light NW winds

Wed: Mix of sun/cloud, FZL in valley, light SW winds

Snowpack Summary

125cm of snow over the last 5 days, along with strong S-SW winds and warm temps, has created a sensitive slab at all elevations. The Dec 13 surface hoar/facets are down 90cm+ and the Dec 7 crust/surface hoar layer is down 100cm+. The Nov 5 crust lingers near the base of the snowpack and several avalanches over the storm period stepped down to it.

Avalanche Summary

A brief respite in the natural avalanche cycle this morning, but we expect it to pick up with the afternoon storm.

A widespread cycle of natural and artillery controlled avalanches up to size 3.5 occurred in the highway corridor (and likely in the backcountry) Saturday morning.

Confidence

Timing, track, or intensity of incoming weather system is uncertain

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.