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Avalanche Forecast

Archived

Feb 20th, 2023–Feb 21st, 2023

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
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.

Regions

North Columbia, South Columbia, Esplanade, Jordan, North Selkirk, Shuswap, West Purcell, Badshot-Battle, Central Selkirk, Goat, Gold, Kokanee, North Okanagan, Retallack, Valhalla, Whatshan.

30 to 50 cm of snow is forecast Monday night into Tuesday morning, which is likely to trigger an avalanche cycle that could reach valley bottom. Travel in avalanche terrain is not recommended.

Confidence

Moderate

Avalanche Summary

Many small to large (size 1 to 2.5) storm slabs and wind slabs were trigered naturally, by exlosives, and riders on Sunday. They generally occurred at treeline and alpine elevations and on all aspects. They were mostly 10 to 50 cm deep, within and at the base of the recent storm snow.

The most recent persistent slab avalanche was reported on Friday, occurring near Revelstoke at 1500 m on a northwest aspect. The avalanche likely released on an old facet and/or surface hoar layer above a melt-freeze crust from late December.

The most recent deep persistent slab avalanche activity was between February 13 and 16, with most avalanches occurring at treelin and alpine elevations on all aspects.

Looking forward, a widespread avalanche cycle is anticipated on Monday night into Tuesday. Human-triggered avalanches are likely for Tuesday. Resulting avalanches could travel to valley bottom. Travel in avalanche terrain is not recommended.

Snowpack Summary

Around 30 to 50 cm of snow is forecast for Monday night into Tuesday, building on the 50 to 100 cm of recent storm snow across the region. All this snow overlies previously wind affected snow in wind-exposed terrain and surface hoar crystals in wind-sheltered terrain around treeline elevations. Wind slabs are likely forming on all aspects at higher elevations from southwest wind switching to northeast wind.

The mid-pack hosts various old layers of surface hoar, facets, and melt-freeze crusts that are slowly bonding to the snowpack. Reports of periodic large avalanches on these layers are a reminder of the complicated snowpack in this region.

A layer of large and weak facets that formed in November is found near the base of the snowpack. The layer is slowly gaining strength but sporadic very large avalanches continue to provide evidence that this layer cannot be trusted.

Weather Summary

Monday Night

Cloudy with snowfall, accumulation 20 to 40 cm, 20 to 40 km/h southwest wind, treeline temperature -7 °C.

Tuesday

Mostly cloudy with snowfall, accumulation 5 to 15 cm, 20 km/h northeast wind, treeline temperature -16 °C.

Wednesday

Mix of sun and cloud with no precipitation, 20 km/h east wind, treeline temperature -22 °C.

Thursday

Mostly clear skies with no precipitation, 20 km/h east wind, treeline temperature -24 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Travel in alpine terrain is not recommended.
  • Very large and destructive avalanches could reach valley bottom.

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.

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.