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Avalanche Forecast

Archived

Apr 11th, 2021–Apr 12th, 2021

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

Regions

Northwest Inland.

Lingering wind slabs may remain reactive to human triggers on lee features below ridgetops in the alpine. Use caution when transitioning into wind affected terrain and avoid slopes with large cornices overhead.

Confidence

High -

Weather Forecast

  

SUNDAY NIGHT: Clear / Light, north ridgetop wind / alpine low temperature -13 / Freezing level valley bottom.

MONDAY: Sunny / Light, southwest ridgetop wind / alpine high temperature 0 / Freezing level 1400 m.

TUESDAY: Mix of sun and cloud / Moderate, west ridgetop wind / alpine high temperature 2 / Freezing level 2000 m.

WEDNESDAY: Sunny / Light, southwest ridgetop wind / alpine high temperature 7 / Freezing level rapidly rising to 2600 m.

Avalanche Summary

Naturally triggered wind slabs on northeasterly aspects in the alpine up to size 2 were reported on Saturday. Additionally, small (size 1) wet loose avalanches on solar aspects were reported at all elevations.

Snowpack Summary

5-20 cm. of recent snow was accompanied by periods of strong winds from shifting directions which formed wind slabs on a variety of aspects at treeline and above. Recent snowfall amounts will vary widely throughout the region due to the convective nature of the spring weather.

The recent snow has covered a variety of snow surfaces, including wind affected snow, crusts on solar aspects and at lower elevations, and soft snow on sheltered slopes at upper elevations.

 Cornices are large, looming, and capable of triggering large avalanches when they fail.

The lower snowpack is reported as well settled and strong in most areas. However, weak facets exist at the base of the snowpack in the more shallow snowpack zones across the region. Where it exists, this layer has the potential to be triggered on steep, rocky slopes with a shallow or thin to thick snowpack; especially with large loads such as a cornice fall.

Terrain and Travel

  • Avoid lee and cross-loaded terrain.
  • Avoid exposure to slopes that have cornices overhead.
  • Minimize exposure to sun-exposed slopes when the solar radiation is strong.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.

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.

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.