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Avalanche Forecast

Archived

Apr 21st, 2021–Apr 23rd, 2021

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

Regions

North Rockies.

A spring diurnal pattern dominates. Wind slabs may exist up high. Danger may increase during the heat of the day.

Confidence

Moderate - Uncertainty is due to the limited number of field observations. Forecast precipitation (either snow or rain) amounts are uncertain.

Weather Forecast

WEDNESDAY NIGHT: Cloudy with snowfall, accumulation 5 to 15 cm and locally more with convective flurries, 40 km/h north wind, alpine temperature rapidly dropping from 0 C to -12 C.

THURSDAY: Morning clouds and afternoon clear skies, 20 km/h north wind, alpine temperature -10 C, freezing level 1000 m.

FRIDAY: Mix of sun and cloud, 20 km/h west wind, alpine temperature -7 C, freezing level 1500 m.

SATURDAY: Mix of sun and cloud, 20 km/h northeast wind, alpine temperature -9 C, freezing level 1200 m.

Avalanche Summary

Avalanche activity has quieted down since the heat wave last weekend. Large loose wet and wet slab avalanches were observed during daytime warming but no new avalanches were observed on Tuesday.

Looking forward, spring-like diurnal conditions are forecast to dominate after Wednesday night's storm. Wind slabs could form during the storm and they may be relatively easy to trigger, as they are likely going to overly a hard melt-freeze crust.

Snowpack Summary

Around 5 to 15 cm of snow is forecast to accumulate by Thursday morning. The snow is expected to fall with strong northerly wind, forming small but potentially touchy wind slabs in exposed terrain features at higher elevations. This snow will overly a hard melt-freeze crust to the mountain tops from recent warm air and sunny skies. The snow may moisten during the heat of the day, particularly on sun-exposed slopes and on all aspects below the freezing level.

A weak basal snowpack is found in many parts of the region, including along the eastern slopes of the Rockies like Core Lodge, Wolverine, Bullmoose, Upper Burnt and perhaps around Mt. Robson. In general, steep, rocky slopes with a shallow or thin to thick snowpack are most suspect and should be avoided.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Wind slabs may be poorly bonded to the underlying crust.
  • Avoid travelling on slopes below cornices.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
  • Back off slopes as the surface becomes moist or wet with rising temperatures.

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.

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.