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Avalanche Forecast

Archived

Nov 20th, 2020–Nov 21st, 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 unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Glacier.

The persistent slab is reaching critical load for both human and natural triggering. Use caution when travelling through runouts

Weather Forecast

5cm new snow is forecast today with moderate westerly wind and freezing levels rising to 1000m. Another 10cm overnight with cooling temperatures will give way to a clear Saturday and Sunday with rising temperatures and wind shifting to the SW.

Snowpack Summary

Up to 70cm of storm snow has formed reactive slabs. The Nov 5th crust is now down 45cm below treeline and up to 1m in the alpine. It can be found, 8cm thick, up to 2500m on all aspects and higher on steep solar aspects. Facets above and below the crust are making this combo an active weak layer with all the recent load over it.

Avalanche Summary

Numerous size 2.5 - 3 avalanches occurred naturally throughout the day yesterday and overnight, initiating in the storm snow, with some stepping down to the Nov 5th crust/facet persistent slab. Field teams ski cut avalanches to size 2 yesterday and there were several Min reports this week of natural, and skier triggered avalanches.

Confidence

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.