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Avalanche Forecast

Archived

Apr 19th, 2021–Apr 21st, 2021

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

Regions

Yukon.

Wet loose avalanches become increasingly likely during the heat of the day. Back off slopes as the surface becomes moist or wet with daytime warming and avoid slopes with large cornices overhead.

Confidence

Moderate - Uncertainty is due to how the snowpack will react to the forecast weather.

Weather Forecast

  

MONDAY NIGHT: Clear / Light, southwest ridgetop wind / alpine low temperature -3 / Freezing level 1000 m.

TUESDAY: Mix of sun and cloud / Moderate, west ridgetop wind / alpine high temperature 1 / Freezing level 1300 m.

WEDNESDAY: Sunny / Strong, north ridgetop wind / alpine high temperature -4 / Freezing level 800 m.

THURSDAY: Sunny / Moderate, north ridgetop wind / alpine high temperature 0 / Freezing level 1300 m.

Avalanche Summary

Avalanche observations were very limited over the weekend. However, numerous naturally triggered wet loose avalanches and cornice failures likely occurred given the very warm weather. Natural avalanche activity will likely decrease as the temperatures cool.

Several naturally triggered wet slab avalanches up to size 2.5 and numerous wet loose avalanches up to size 2 were reported on Thursday. See MIN.

Keep in mind that periods of rapid warming can weaken deeply buried weak layers and increase the likelihood of large natural avalanches.

Snowpack Summary

Successive days of temperatures well above 0 at mountain tops have created moist surfaces at all elevations/aspects. Clear skies and cooling temperatures will form firm crusts overnight which will lock up the snowpack until the surface crust melts. Avalanche danger can increase rapidly after the sun melts the frozen snow surface and begins to penetrate deeper into the snowpack. Strong solar radiation and warming often trigger wet loose avalanches and large cornice failures. Cornice falls could trigger large avalanches on deeply buried weak layers. 

While there have not been many weak layers of concern this season, Keep in mind that periods of rapid warming can weaken deeply buried weak layers and increase the likelihood of large natural avalanches.This will more likely be an issue in shallow snowpack areas like the Wheaton compared to the thicker and stronger snowpack around White Pass.

Terrain and Travel

  • Avoid travelling on slopes below cornices.
  • The more the snowpack warms-up and weakens, the more conservative you`ll want to be with your terrain selection.
  • Back off slopes as the surface becomes moist or wet with rising temperatures.
  • If triggered loose wet avalanches may step down to deeper layers resulting in larger avalanches.

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.