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Avalanche Forecast

Archived

Apr 15th, 2021–Apr 16th, 2021

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 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, human triggered possible.

Regions

Northwest Coastal.

 

Sustained warming continues to increase the likelihood for large cornice failures and wet loose avalanches. Start early and plan to be off large slopes before the heat of the day.

Check out the latest Forecaster's Blog for more information on managing current conditions.

Confidence

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

Weather Forecast

  

THURSDAY NIGHT: Clear / Light, southeast ridgetop wind / alpine low temperature 4 / Freezing level 3000 m.

FRIDAY: Sunny / Light, south ridgetop wind / alpine high temperature 9 / Freezing level 3000 m.

SATURDAY: Sunny / Light, southwest ridgetop wind / alpine high temperature 8 / Freezing level 3000 m.

SUNDAY: Sunny / Moderate, east ridgetop wind / alpine high temperature 2 / Freezing level dropping to 2000 m.

Avalanche Summary

Warm sunny weather this week will cause wet loose avalanches and cornice failures.

Numerous naturally triggered wet loose avalanches up to size 3 and cornice failures to size 2.5 were reported on Wednesday.

Snowpack Summary

Lingering wind slabs may still be reactive in isolated locations on steep northerly aspects in the alpine. All other terrain is undergoing a melt-freeze cycle with successive days of warm sunny weather. 

Strong solar radiation and warming will likely trigger the large cornices that hang over ridgelines. Cornice falls could trigger large avalanches on the slopes below.

The snowpack is overall strong and settled in most areas, however, sustained warming can increase the likelihood of large avalanches failing on deeply buried weak layers.This is most likely to occur on steep, rocky alpine slopes with a shallow or thin to thick snowpack.

Glide cracks releasing as full depth glide slab avalanches become more common in the spring and are extremely difficult to predict. Best practice is to avoid slopes with glide cracks.

Terrain and Travel

  • Extra caution is needed around cornices under the current conditions.
  • Avoid exposure to slopes that have cornices overhead.
  • As surface loses cohesion due to melting, loose wet avalanches become common in steeper terrain.
  • Back off slopes as the surface becomes moist or wet with rising temperatures.

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.

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.