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Archived

Avalanche Forecast

Apr 11th, 2021–Apr 12th, 2021
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
1: Low
The avalanche danger rating at treeline will be low
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable

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.

Avalanche Problems

Wind Slabs

Lingering wind slabs formed by 10-20 cm. of recent snow and previously strong winds from shifting directions may remain reactive on lee features in the alpine.

Aspects: All aspects.

Elevations: Alpine.

Likelihood: Possible

Expected Size: 1 - 2

Cornices

Cornices are large and looming along many ridgelines and have likely grown with the recent wind. 

Strong solar radiation and warming are common triggers for cornice failures which could trigger large avalanches.

Aspects: North, North East, East, South East, North West.

Elevations: Alpine.

Likelihood: Possible

Expected Size: 1.5 - 2.5

Loose Wet

Small wet loose avalanches may start to run naturally on steep solar aspects when the sun comes out.

Aspects: East, South East, South, South West, West.

Elevations: All elevations.

Likelihood: Possible - Likely

Expected Size: 1 - 1.5