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Avalanche Forecast

Archived

Nov 20th, 2021–Nov 21st, 2021

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

Regions

Jasper.

Strong west to south-west winds expected to add load to the recently formed wind slabs and persistent slab as there is still a lot of snow available for transport.

Weather Forecast

Sunday: Cloudy with isolated flurries. Precip: Trace. Alp temperature: High -7 C. Ridge wind southwest: 20-35 km/h.Monday: Snow: 9 cm. Alpine temperature: Low -10 C, High -5 C. Wind southwest: 20-40 km/h. FL: 1400 metres.Tuesday: Cloudy with scattered flurries: 4 cm. Alp temp: Low -13 C, High -7 C. Wind west: 15 km/h gusting to 45 km/h.

Snowpack Summary

Surface hoar of up to 4mm observed on all aspects up into alpine prior to the current strong W- SW winds. The storm snow has now formed persistent slab particularly in wind loaded features. A 2cm thick crust 80cm down is found up to 2500m or higher. Weak facets below the crust result in sudden collapse test results.

Avalanche Summary

Friday's team observed two size 2 persistent slab avalanches on windloaded features in the alpine and treeline. On Wednesday numerous avalanches up to size 3.5, generally from steep alpine features, were noted. They occurred during or at the end of the Nov 13-15th storm. One 800m wide avalanche was caused by explosives at tree-line on Tuesday.

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.

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.