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Avalanche Forecast

Archived

Jan 27th, 2022–Jan 28th, 2022

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

Regions

North Columbia.

Wind slabs may remain reactive to human triggering in exposed high elevation terrain. There is ongoing concern for the early-December deep persistent problem and we are now in a period of low probability, high consequence with this layer.

Confidence

High - Confidence is due to a stable weather pattern with little change expected.

Weather Forecast

The ridge of high pressure brings two more days of dry and sunny conditions before the next storm system arrives Saturday night bringing snowfall for Sunday. 

Thursday Night: Mainly clear with valley cloud, light SW wind, treeline temperature around -10 °C.

Friday: Sunny with valley cloud, light SW wind, treeline high around -4 °C.

Saturday: Increasing cloud cover, moderate SW wind, treeline high around -4 °C.

Saturday night and Sunday: Snowfall 15-25 cm, moderate SW wind, treeline high around -3 °C.

Avalanche Summary

On Wednesday, two size 1.5-2 wind slabs were observed and several cornice failures triggered slabs up to size 2 on NE-NW aspects. Some loose avalanches up to size 1.5 were also observed on a SW aspect. On Tuesday, a natural size 1.5 persistent slab was reported on an E aspect at 1900 m in the Monashees north of Revelstoke failing down 30-45 cm. A natural size 2 cornice failure was reported on an E aspect at 2600 m. On Monday, wind/storm slabs avalanches up to size 1.5 were reported throughout the region. Two natural size 2.5-3 deep persistent slab avalanches were also reported which released on the December facet/crust layer. 

Between January 20 and 23, numerous very large (size 2.5-4.5) deep persistent slab avalanches occurred. These avalanches failed on the early December facet/crust layer, typically 100-150 cm deep. 

Snowpack Summary

The snow surface is highly variable and consists of a crust at lower elevations and on solar slopes extending into the alpine, wind affected surfaces and wind slabs in exposed terrain, and settling powder in sheltered areas on polar aspects. Ongoing surface hoar growth up to 12 mm has also been reported to be widespread in sheltered areas which is expected to be most prominent at elevations near the top of the valley fog layer.

There are three prominent layers in the upper snowpack which are mainly dormant now but could still create a problem during the next storm or warming event. The storm on Jan 20 covered a layer of surface hoar which is now down 20-30 cm. A layer of facets and surface hoar from early January is now down around 40-60 cm. A thick layer of facets from the cold drought end of December is now down close to 1 m. 

The primary weak layer that remains a widespread concern across the Columbia Mountains is a deeply buried crust/facet layer that formed in early December. It is typically down 100-180 cm, but as deep as 250 cm in wind-loaded terrain. This layer is likely to plague our snowpack for the remainder of the season and will be a low probability but extremely high consequence result if triggered.

Terrain and Travel

  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Conditions may have improved, but be mindful that deep instabilities are still present.

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.