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Avalanche Forecast

Archived

Jan 11th, 2021–Jan 12th, 2021

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

Regions

Banff Yoho Kootenay.

The avalanche hazard will gradually increase over the next two days as a warm storm arrives with a lot of wind. Watch for increased wind loading in overhead start zones and pull back into more conservative terrain as the snow arrives.

Weather Forecast

5 cm of new snow is expected on Tuesday during the day with another 10-20 cm Tuesday night into Wednesday morning. Alpine winds will remain in the Strong to Extreme range out of the SW throughout the storm. Temperatures are looking fairly warm. -4 to -2 C at treeline and around -6 C in the alpine which could result in rapid slab development. 

Snowpack Summary

A couple cm's of new snow mixed with facets and surface hoar on the surface. Thin suncrust on some steep solar aspects. Wind effect in alpine areas. Three persistent weak layers from Dec are down 30-100 cm. These have generally been unreactive but occasionally result in hard sudden planar shears. The Nov. 5 basal crust/facets are currently dormant.

Avalanche Summary

Little avalanche activity Monday. A powder cloud was observed on the East face of Mt Temple that may have been triggered by the wind. One cornice triggered size 2 slab avalanche was observed in the alpine on Mt Field from the last 48 hours. A skier triggered size 0.5 slab in a very steep open glade just below treeline on Mt Field was also observed.

Confidence

Forecast snowfall amounts are uncertain on Wednesday

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.