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Avalanche Forecast

Archived

Jan 11th, 2023–Jan 12th, 2023

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

Regions

Kootenay Boundary, Bonnington, Kootenay Pass, Norns, Rossland, South Okanagan, Ymir.

Expect storm slab reactivity to increase throughout the day as new snow accumulates and winds increase. Avoid shallow, variable, rocky slopes where deep weak layers remain a major concern.

Confidence

Moderate

Avalanche Summary

A number of natural and rider-triggered storm slab avalanches have been reported since Monday. Several of these have released on a layer of preserved surface hoar roughly 30 cm below the surface.

Evidence of instabilities deep in the snowpack continue to be reported. On Tuesday an avalanche was triggered by a snowcat around 1800 m. Although it did not propagate, it did fail deep, near the base of the snowpack.

Please continue to share any observations or photos on the Mountain Information Network.

Snowpack Summary

Expect surface slab development throughout Thursday with forecast snow and wind. This will further bury a layer of large surface hoar in wind-sheltered terrain, down 30 to 40 cm. A melt-freeze crust is buried by roughly 60 to 80 cm. This crust ranges from 2 cm at higher elevations to 10 cm at lower elevations. Below the crust, the mid-snowpack is generally well consolidated. A weak layer of facets and a crust near the bottom of the snowpack remains a concern.

Treeline snow depths are roughly 150 to 200 cm.

Weather Summary

Wednesday night

Mostly cloudy, with no precipitation. Light to moderate ridgetop winds. Treeline temperatures 0 to -5 C.

Thursday

Cloudy with light snow, 5 to 10 cm. Moderate south ridgetop winds. Treeline temperature 0 to -5 C.

Friday

Cloudy with snow. 10 to 25 cm overnight, and another 5 to 10 cm throughout the day. Moderate to strong south ridgetop winds. Treeline temperatures around 0 C. Freezing levels 2000 m.

Saturday

Cloudy with snow, 10 to 15 cm. Moderate south ridgetop winds. Treeline temperatures around 0 C. Freezing levels 1500 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Watch for fresh storm slabs building throughout the day.
  • Closely monitor how the new snow is bonding to the old surface.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.