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Avalanche Forecast

Archived

Nov 21st, 2020–Nov 22nd, 2020

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

Regions

Glacier.

Do not let good visibility and great skiing entice you to ski bigger lines.  The Nov. 5th crust/facet persistent weak layer is ripe for catching skiers off guard.

Weather Forecast

Unsettled air will give mostly cloudy skies and isolated flurries through the weekend.  A system making landfall from the NW Monday and will give snowfall early in the week.

Today: Alpine High -8 °C. Ridge wind(RW) light SW. Freezing level (FzL): 1100m.

Tonight: Low -9 °C. RW light S.

Sunday: High -5 °C. RW Light. FzL: 1200m.

Snowpack Summary

Up to 70cm of storm snow and Southwesterly winds has formed reactive slabs. The Nov 5th crust is now down buried over 1m deep in most starting zones. This crust is 8cm thick, and can be found up to 2500m on all aspects. Facets above and below the crust are making this combo an active weak layer that will persist for the foreseeable future.

Avalanche Summary

Large natural avalanches continue to occur as ongoing snowfall and wind progressively overloads the snowpack. These are generally initiating in the storm snow, with some stepping down to the Nov 5th crust/facet combo. There were several Min reports this week of natural, and skier triggered avalanches, as well as large whumphs in open terrain.

Confidence

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.

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.