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Avalanche Forecast

Archived

Nov 19th, 2020–Nov 20th, 2020

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

Banff Yoho Kootenay.

New snow, wind, and a weak layer of crust and facets are making the snowpack more complex. Time to dial back terrain choices. Good ski conditions in sheltered areas that are deep enough to cover the rocks! SH

Weather Forecast

5-10cm expected on Friday, with increasing winds at upper elevations to strong from the S/SW. Temperatures -10 in the valley warming to -5C, and -12 to -15C in the alpine.

Snowpack Summary

15-30 cm snow over the last few days with new and buried windslabs existing in alpine and treeline. The Nov. 5 Facets/crust combo is 20-40 cm off the ground and is buried 40-70cm producing variable test results. It extends up to 2400m on shady aspects and higher on solar aspects. Total snow depths at treeline are 50-100 cm.

Avalanche Summary

Avalanche control on 93S yesterday produced a few slides up to size 2. Lake Louise ski patrol were able to trigger a size 2 wind slab in N facing terrain that hadn't had previous control. Skier remote report sz 1.5 today on facets to ground (40cm deep) at 2000m, 80m wide near Watermelon peak. Other audible avalanches heard but poor visibility.

Confidence

Due to the number and quality 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.

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.

Loose Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.