Avalanche Forecast

Archived

Jan 25th, 2024–Jan 26th, 2024

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 and human triggered avalanches likely.

Below Treeline

Natural avalanches possible, human triggered probable.

Regions

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

Mt Stephen will be closed for avalanche control Friday.

Elevated winds, mild temperatures, and snowfall have led to the development of slabs at all elevation bands.

These slabs are likely to be found sitting on weak layers.

As freezing levels rise through the weekend, expect these slabs to become more sensitive to human triggering.

Confidence

Moderate

Avalanche Summary

Wednesday: Sunshine Village avalanche control triggered a sz 2 slab with a ski cut in thin, steep SW facing terrain at 2550m this was thought to be triggered on re-loaded basal facets.

Thursday: Lake Louise avalanche control continued to work with small soft slabs sitting over facets - occasionally these have pulled deeper into the basal facets over the last few days. Bourgeau Left-hand ran sz 2.5 today with a crown though to be about 50cm deep.

Snowpack Summary

Hard and soft slabs have formed due to recent warming, strong winds, and small snow inputs. These slabs may overlie two weak layers: 1) Facets from the cold snap sit 10 to 30cm deep. 2) Surface hoar or a sun crust have been found in some areas below the facets 30 to 50cm deep.

The midpack offers some strength and features two crusts that persist as high as 2350m.

The lower part of the snowpack comprises weak facets and depth hoar.

Weather Summary

Friday freezing levels will be just above Valley Bottom as W winds increase to strong.

Freezing levels will return to VB overnight Friday as winds increase further and shift SW.

Saturday winds should diminish to strong as freezing levels rise to 1800m.

Sunday freezing levels as high as 2400m are expected as winds increase to extreme.

Scattered flurries are expected for the period.

Terrain and Travel Advice

Avoid areas where the snow feels stiff and/or slabby.
Avoid shallow snowpack areas, rock outcroppings and steep convex terrain where triggering is most likely.
The likelihood of deep persistent slab avalanches will increase with each day of warm weather.

Problems

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.