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Avalanche Forecast

Archived

Jan 26th, 2022–Jan 27th, 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 unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

South Columbia.

Wind slabs 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 low probability, high consequence scenario with this layer. 

Confidence

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

Weather Forecast

The ridge of high pressure is currently forecast to persist until Saturday with the next storm system arriving Saturday night. 

Wednesday Night: Mainly clear with lingering valley cloud, light variable wind, treeline temperature around -8 °C.

Thursday: Mainly sunny with valley cloud, light SW wind, treeline high around -3 °C.

Friday: Mainly sunny with valley cloud, light SW wind, treeline high around -3 °C.

Saturday: Increasing cloud cover, light to moderate SW wind, treeline high around -3 °C.

Avalanche Summary

On Tuesday, a variety of natural wind/storm slabs up to size 2 and cornices up to size 3 were reported but most of this natural activity had occurred on Monday or Sunday.

On Monday, wind slab avalanches on cross-loaded lee slopes produced natural avalanches up to size 2. A size 2.5 glide slab released near Revelstoke on south alpine slope due to strong solar input. Explosive control triggered a deep persistent size 3 avalanche in the Monsahees, with a fracture line of 120 cm deep.

Around Silverton area, a natural size 3 avalanche was reported Sunday on steep alpine feature. The failure was down to 100-150 cm the December facet/crust layer and ran full path. See the MIN report here. 

Over the past week, numerous very large (size 2.5-4.5) deep persistent slab avalanches occurred in both the Selkirks and Monashees. These avalanches failed on the early December facet/crust layer, typically 100-150 cm deep. 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.

Snowpack Summary

The snow surface is highly variable and consists of a crust at lower elevations and on solar slopes 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 10 mm has also been reported in sheltered areas which is expected to be most prominent at elevations near the top of the valley fog layer.

The top 50-100 cm of the snowpack has a variety of persistent layers that may or may not remain a problem. The most recent snowfall 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. The layer of facets from the 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 100-150 cm, but as deep as 200 cm in wind-loaded terrain. There has been regular avalanche activity on this layer at all elevations for over a month, but we are now seeing decreasing evidence since the recent warming event.

Terrain and Travel

  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Conditions may have improved, but be mindful that deep instabilities are still present.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.

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.