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Avalanche Forecast

Archived

Dec 24th, 2020–Dec 25th, 2020

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

Regions

Banff Yoho Kootenay.

http://www.pc.gc.ca/apps/links/goto_e.asp?destination=http://avalanche.ca/spaw/2020-12-23-spaw

It's a tricky snowpack in many parts of the forecast region with a lot of variability with recent winds, snowfall and multiple weak layers.

There is a Special Avalanche Warning in effect. Click Here to access.

Merry Christmas!

Weather Forecast

Friday will be sunny with an alpine inversion and moderate to strong southwest alpine winds. Alpine temperatures will be in the -5 to -10 range whereas the valleys will stay colder. Saturday and Sunday we'll see light winds, light snow and temperatures in the -5 to -15 range.

Snowpack Summary

Winds from a variety of directions have blown the 30-60cm of snow from the past week into wind slabs at higher elevations. The Dec 13 and Dec 7 sun crust/surface hoar/facet layers are down ~ 50cm and ~80 cm respectively. The decomposing Nov crust/facets sits at the bottom of the snowpack. Height of snow at tree line is 80-150cm.

Avalanche Summary

Avalanche control this week produced mixed results from no result to size 3. Most were storm slabs, sometimes stepping down to persistent layers. A few deeper releases on the Nov 5th crust/facets Tuesday including a skier remote in the Watermelon Peak area. Reports of explosive controlled new wind slabs from the ski hills today.

Confidence

Due to the number of field observations

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.