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Avalanche Forecast

Archived

Apr 19th, 2021–Apr 20th, 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 possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Purcells.

The best and safest riding will be in north-facing terrain that is free from cornices overhead. Avalanche danger will be MODERATE when slopes are exposed to the sun.

Confidence

Moderate - Uncertainty is due to rapidly fluctuating freezing levels.

Weather Forecast

Warm sunny weather continues until a weak frontal system arrives on Thursday.

TUESDAY NIGHT: Clear skies, light northeast wind, freezing level drops to valley bottom with treeline temperatures dropping to -6 C.

MONDAY: Sunny, light wind, freezing level climbs to 2200 m with treeline temperatures reaching 0 C.

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

THURSDAY: Scattered flurries bring 5-10 cm of snow above 1800 m and light rain in the valleys, moderate northeast wind, freezing level around 1800 m with treeline temperatures around -2 C.

Avalanche Summary

Multiple days of above freezing temperatures resulted in widespread size 1-2 wet loose avalanches on sun-exposed slopes between Thursday and Saturday. There were also likely a few larger wet slab avalanches during this period, such as the one reported near the Bugaboos on Saturday in this MIN report. There were also natural cornice failures over this period, some as big as size 3. The last report of a persistent slab avalanche was from March 8 in the Golden area where a cornice fall triggered a size 3 avalanche on an steep east-facing slope in the alpine.

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

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 a 30-60 cm deep crust layer 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.