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Avalanche Forecast

Archived

Dec 22nd, 2020–Dec 23rd, 2020

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.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Glacier.

As the sky clears from a stormy week, a cautious approach to the backcountry is needed. Reactive storm slabs sit atop weak surface hoar and crusts. How well the new snow bonds to these layers will determine danger levels over the next few days.

Weather Forecast

A building high pressure ridge will dry the region out over the next few days.

Today: Cloudy with sunny periods, nil snow, ALP high -11*C, light/mod NW winds

Wed: Mix of sun/cloud, ALP high -4*C, light W winds

Thurs: Sunny with cloudy periods, ALP high -3*C with temp inversion in valley bottom, light SW winds

Snowpack Summary

140cm of snow over the last 6 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 140cm+ and the Dec 7 crust/surface hoar layer is down 150cm+. The Nov 5 crust lingers near the base of the snowpack and several avalanches over the storm period stepped down to it.

Avalanche Summary

Artillery slab avalanche results to sz 4, including the Fidelity path reaching the valley floor last night. Suspect wide slab propagation on many alpine and tree-line start zones, likely on our persistent weak layers. Natural activity has decreased with the passage of the storm front, but N'ly winds are keeping S aspects active (ie. Mt Tupper).

Confidence

Due to the number of field observations

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.