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Avalanche Forecast

Archived

Apr 21st, 2021–Apr 22nd, 2021

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

Purcells.

Be careful around cornices and watch for new snow forming isolated wind slabs in the alpine.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

A cold front crossing the region on Thursday will bring a shift to cooler stormy weather.

WEDNESDAY NIGHT: Increasing clouds, 40 km/h northwest wind, freezing level drops to 1200 m with treeline temperatures dropping to -4 C.

THURSDAY: Cloudy with light flurries bringing up to 5 cm of snow across the region, light northeast wind, freezing level climbs to 1600 m with treeline temperatures around -3 C.

FRIDAY: Cloudy with scattered flurries bringing 5-15 cm of new snow, flurries easing in intensity throughout the day, light southwest wind, freezing level climbs to 1800 m with treeline temperatures around -2 C.

SATURDAY: Cloudy with scattered flurries bringing another 5-10 cm of snow, light southeast wind, freezing level climbs to 1800 m with treeline temperatures around -2 C.

Avalanche Summary

Warm temperatures over the past week resulted in widespread wet avalanche activity, primarily on sun-exposed slopes. Most of the activity was size 1-2 wet loose avalanches, but a few larger and destructive wet slab avalanches were reported (near the Bugaboos on Saturday and near Golden on Monday). Some large cornice falls were also observed.

The cooling trend will make wet avalanches problems less likely in the coming days, making isolated wind slabs and cornice falls the primary concern.

Snowpack Summary

A dusting of new snow will sit above a thick surface crust. The upper snowpack has been undergoing a daily melt-freeze cycle, so with the cooling temperatures a hard crust will form everywhere except in high north-facing terrain where there still may be dry snow above roughly 2300 m. We suspect older weak layers have gone inactive as the weather patterns over the past month have been favourable for strengthening the snowpack.

Terrain and Travel

  • When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.
  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
  • Wind slabs may be poorly bonded to the underlying crust.

Problems

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.

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.