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Avalanche Forecast

Archived

Nov 23rd, 2020–Nov 24th, 2020

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

Regions

Glacier.

A conservative approach to terrain selection remains key to managing the persistent avalanche problem.

Weather Forecast

An Aleutian Low is pushing weather systems our way, culminating with the passage of a cold front late Tuesday.

Today: Mostly cloudy with flurries. Alpine High -7 C. Ridge wind (RW) light SW. Freezing level (FzL) 1100m.

Tonight: Flurries (2cm). Low -8. RW moderate SW.

Tuesday: Snow, heaviest in the evening (15-25cm). High -6. RW Strong SW. FzL 1200m.

Snowpack Summary

Southerly winds in the high alpine have built fresh slabs in immediate lees. The Nov 5th crust is now buried over 1m in most starting zones. This crust complex is over 8cm thick, and can be found up to 2500m on all aspects; with facets above and below this is an active weak layer that will persist for a long time.

Avalanche Summary

No fresh avalanches observed since early Saturday morning.

Large natural avalanches were triggered by last weeks snowfall in the highway corridor. Several of these failed on the Nov 5th crust/facet layer.

There are several Min reports of natural, and skier triggered avalanches that occurred during last weeks storm.

Confidence

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

Problems

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.

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.