Avalanche Forecast

Archived

Mar 29th, 2021–Mar 30th, 2021

Alpine

Natural avalanches possible, human triggered probable.

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.

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.

Storm slabs may remain reactive to human triggers as natural avalanche activity tapers off. Start with small terrain features, look for sign of instability and gather information before considering bigger terrain.

Confidence

Moderate -

Weather Forecast

Monday night: Scattered flurries. Light to moderate northwest wind. Freezing level valley bottom. Alpine temperature -13.

Tuesday: Scattered flurries. Light to moderate northwest wind. Freezing level 1400 m. Alpine temperature -9.

Wednesday: Sunny. Light southwest wind. Freezing level 2000 m. Alpine temperature -1.

Thursday: Sunny. Moderate southwest wind. Freezing level 2000 m. Alpine temperature -1.

Avalanche Summary

Preliminary reports of avalanche activity during the storm include one visually observed and numerous audible natural storm slabs suspected to be in the size 3-3.5 range in the southeast corner of the region.

Notable reports of avalanche activity prior to the storm include:

A size 3 slab avalanche was observed northeast of Revelstoke on Wednesday. The avalanche failed on the ground on a south aspect at 1600 m.
In neighboring Glacier National Park and South Columbia regions, several natural cornice falls triggered deep slab avalanches size 2-3.

Snowpack Summary

The weekend's storm dropped 20-50 cm over the Selkirk mountains in the south of the region and 5-10 cm elsewhere. This snow came with wind from southwest to northwest, loading thick slabs in lee features at upper elevations. Reports from Monday have indicated that the new snow is bonding well with underlying surfaces. Crusty and/or moist surfaces exist below treeline depending on elevation and time of day.

At alpine and treeline elevations, a widespread crust exists (except on north-facing slopes above 1800 m) buried 50-100 cm deep. Overall the snow seems to be bonding well at this interface, although there have been a few isolated avalanches running on crust layers over the past few week.

Terrain and Travel

Keep in mind that human triggering potential persists as natural avalanching tapers off.
Start with conservative lines and watch for clues of instability.
Seek out sheltered terrain where new snow hasn't been wind-affected.
Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.