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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 Inland.

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 your 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 extreme winds on Saturday. On Sunday, natural avalanche activity is expected to taper-off with forecast cooling and clearing. That said, newly formed wind slabs may remain ripe for human triggering for the next few days.

Snowpack Summary

Reactive wind slabs are expected to form as a result of snow and extreme westerly winds on Saturday. The reactivity of these new wind 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 may have occurred on shaded terrain. If you've been in the mountains, please share your observations on our Mountain Information Network.

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.