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Avalanche Forecast

Archived

Nov 21st, 2015–Nov 22nd, 2015

Alpine
Below Threshold.
Treeline
Below Threshold.
Below Treeline
Below Threshold.
Alpine
Below Threshold.
Treeline
Below Threshold.
Below Treeline
Below Threshold.
Alpine
Below Threshold.
Treeline
Below Threshold.
Below Treeline
Below Threshold.

Regions

Northwest Coastal.

Snowfall and extreme winds are expected to increase the Avalanche Danger. Conservative terrain selection is highly recommended. Forecasters are working with very little field data at this time. Please share you observations on the MIN.

Weather Forecast

Throughout Sunday we can expect a clearing trend with freezing levels eventually falling to valley bottom. Extreme westerly winds are also expected to shift to moderate and northwesterly as a dry arctic ridge develops for Monday and Tuesday.

Avalanche Summary

A natural avalanche cycle is expected to occur in response to new snow and wind on Saturday. On Sunday, natural avalanche activity is expected to taper-off with forecast cooling and clearing. That said, the newly formed storm slab may remain ripe for human triggering for the next few days.

Snowpack Summary

Deep and destructive storm slabs are expected to form as a result of Saturday's storm, especially in the north of the region where total accumulations are expected to be the highest. The reactivity of these new storm slabs will likely change with elevation and underlying snowpack structure. Due to limited observations, I have very little confidence in what that underlying structure may be, although faceting and surface hoar development have been reported on shaded terrain. If you've been in the mountains, please share your observations on our Mountain Information Network.

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.