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Avalanche Forecast

Archived

Apr 1st, 2021–Apr 2nd, 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, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Northwest Inland.

Moderate to strong winds from shifting directions are forming fresh wind slabs on lee features at treeline and above on a variety of aspects. Stay alert to changing conditions with elevation and aspect to avoid wind loaded slopes.

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

  

THURSDAY NIGHT: Cloudy with flurries; 3-5 cm. / Strong, southwest ridgetop wind / alpine low temperature -11 / Freezing level valley bottom.

FRIDAY: Snow/rain; 3-10 mm, and another 5-10 cm. overnight / Strong, southwest ridgetop wind / alpine high temperature -2 / Freezing level 800 m.

SATURDAY: Cloudy with isolated flurries; 0-3 mm. / Light, south ridgetop wind / alpine high temperature -1 / Freezing level 900 m.

SUNDAY: Mix of sun and cloud / Strong, northwest ridgetop wind / alpine high temperature -1 / Freezing level 900 m.

Avalanche Summary

On Wednesday, naturally triggered wet loose avalanches up to size 1.5 were reported on steep solar aspects.

Snowpack Summary

Moderate to strong winds from shifting directions are forming fresh wind slabs on lee features at treeline and above on a variety of aspects. A firm crust exists at lower elevations.

Buried 70-120 cm. deep, a spotty layer of surface hoar may exist on sheltered north aspects, as well as a crust on south aspects and below 1500 m. Recent observations suggest that this interface is bonding.

The mid and 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 within much of the region and have 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

  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Avoid freshly wind loaded terrain features.
  • Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
  • Caution around slopes that are exposed to cornices overhead.

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.