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Avalanche Forecast

Archived

Nov 20th, 2024–Nov 21st, 2024

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

Regions

Banff Yoho Kootenay, Little Yoho, Banff, East Side 93N, Kootenay, Lake Louise, LLSA, Sunshine, West Side 93N, Field.

Continuing snowfall at 2-4 cm/day is building the Rockies snowpack. Several days of cold temperatures and light winds, from the east on Wed, have left 5-10 cm of soft snow on the surface. But, evidence of a proper weak layer at the base of the snowpack (crust/facets) also continues to emerge daily, with fresh avalanches on the ground.

Confidence

Moderate

Avalanche Summary

Lake Louise ski patrol reported another size 2 avalanche failing on the Oct crust (right above the ground) at 2470 m on a SE aspect (alpine terrain). This is the third day in a row with this kind of avalanche released with an explosive. Also, a few size 1's on the Nov 9 crust but no new windslabs.

Snowpack Summary

5-15 cm of soft surface snow sits over an early season snowpack ranging from 40-60 cm at treeline. Two weak layers exist: a Nov 9 crust/surface hoar about 25 cm above the ground, and an Oct crust/facet layer right above the ground. Avalanches have been failing on the Oct crust in alpine areas with explosives. We have minimal early season observations of how widespread this layer is, but we think the Oct crust is in most places at treeline and above.

Weather Summary

Currently a "bomb cyclone" is offshore of Vancouver Island, and an Arctic cold front is descending from the north and out on the prairie—this is our recipe for snow, which will be continuous but light through the weekend. Expect up to 5 cm a day and 10-15 by the weekend, with temperatures around -10 and generally light winds.

Terrain and Travel Advice

  • Shooting cracks, whumpfs, and recent avalanches are strong indicators of an unstable snowpack.
  • Avoid steep terrain, including convex rolls, or areas with a thin, rocky, or variable snowpack.

Problems

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.