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Avalanche Forecast

Archived

Apr 20th, 2021–Apr 21st, 2021

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

Regions

Purcells.

One more day of warm sunny weather before cool cloudy weather arrives. Avoid sun-exposed slopes on Wednesday.

Confidence

Moderate - Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

TUESDAY NIGHT: Clear skies, light northwest wind, freezing level drops to valley bottom with treeline temperatures dropping to -3 C.

WEDNESDAY: Sunny with some clouds in the afternoon, light northwest wind with some moderate gusts in the afternoon, freezing level climbs to 2400 m with treeline temperatures reaching +2 C.

THURSDAY: Scattered flurries bring 5-15 cm of snow above 1500 m and light rain in the valleys, light southeast wind, freezing level around 1500 m with treeline temperatures around -3 C.

FRIDAY: Mix of sun and cloud with some isolated flurries, light wind, freezing level climbs to 1900 m with treeline temperatures reaching -1 C.

Avalanche Summary

Multiple days of above freezing temperatures resulted in widespread wet loose and wet slab avalanches on sun-exposed slopes over the past week. The most recent observations are from the Dogtooth Range on Monday, where several large wet slab and wet loose avalanches released. There was also a large wet slab avalanche reported near the Bugaboos on Saturday in this MIN report. There were also natural cornice failures triggered by warming over the past week, some as big as size 3. 

You can still expect wet loose avalanches and cornice falls on Wednesday, but they will be less widespread and destructive than they were over the weekend due to the relatively cooler temperatures and thicker surface crusts.

Snowpack Summary

A surface crust will form overnight and then gradually break down with daytime warming. Dry snow may still be found in high north-facing terrain (above roughly 2300 m). While there have been no recent avalanches on buried weak layers, there are a few layers that could potentially be triggered during periods of intense warming or by a large cornice fall. This includes 30-60 cm deep crust layers from mid-March and the early November crust near the bottom of the snowpack.

Terrain and Travel

  • Avoid being on or under sun exposed slopes.
  • 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.

Problems

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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.