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Avalanche Forecast

Archived

Nov 27th, 2021–Nov 28th, 2021

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

Regions

Yukon.

Strong southwesterly winds have formed large wind slabs reactive to human triggers.

Persistent slabs may be possible to trigger on a crust near the bottom of the snowpack. See Mountain Information Network (MIN) report.

Confidence

Low - Uncertainty is due to the limited number of field observations.

Weather Forecast

SATURDAY NIGHT: Mostly cloudy with isolated flurries; 0-3 cm / Moderate, southwesterly winds / Low of -14

SUNDAY: Snow; 5-10 cm / Strong, southwesterly winds / High of -11

MONDAY: Mix of sun and cloud / Strong, southerly winds / High of -10

TUESDAY: Cloudy with flurries; 3-5 cm / Strong, southwesterly winds / High of -10

Avalanche Summary

Strong southwesterly winds have formed large wind slabs reactive to human triggers on lee features.

With uncertainty about the snowpack structure, it may also be possible to trigger large avalanches from thin areas on big alpine slopes. Until there is more information about the snowpack we recommend an extra-cautious approach and careful snowpack evaluation, especially in high-consequence terrain.

Snowpack Summary

30+ cm of recent storm snow and strong southwesterly winds have formed thick wind slabs reactive to human triggers.

A persistent weak layer of facets over a crust near the bottom of the snowpack has been reported as being reactive to human triggers near Fraser. See MIN HERE.

Terrain and Travel

  • Avoid freshly wind loaded terrain features.
  • Use ridges or ribs to avoid areas of wind loaded snow.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Avoid shallow snowpack areas, rock outcroppings and steep convex terrain where triggering is most likely.

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.

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.