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Avalanche Forecast

Archived

Jan 18th, 2020–Jan 19th, 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 unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Banff Yoho Kootenay.

Windy and warm on Sunday which may cause a spike in natural activity. Limit exposure to overhead terrain while the winds are strong, and don't forget about the deeper weak layers when considering your terrain choices.

Weather Forecast

The big story is increasing temperatures Sunday (Alpine lows of -10 to -12C and highs of -2 to -4C), and continued strong winds in the alpine from the W/SW.  Temperatures moderate on Monday with up to 10cm of snow Tuesday/Wednesday.

Snowpack Summary

2-15cm of new snow in the past 24 hrs (highest amounts on Hwy. 93N)and sustained Southerly winds continue to build wind slabs in the alpine and open areas at tree line. There is up to 60 cm above the Dec 31 layer of facets, surface hoar and sun crust. Concern remains for the weak layers of facets and depth hoar near the base of the snowpack.

Avalanche Summary

Numerous avalanche observations and reports yesterday across the region up to Sz 2.5. Natural cornice failures, wind and persistent slabs have come become reactive with the recent dramatic swing in temperatures. Local ski areas seeing smaller reactive wind slabs to size 2 in the alpine and treeline.

Confidence

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.