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Avalanche Forecast

Archived

Apr 21st, 2021–Apr 22nd, 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.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.

Regions

Northwest Inland.

 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

High -

Weather Forecast

  

WEDNESDAY NIGHT: Mostly clear / Moderate, northwest ridgetop wind / alpine low temperature -5 / Freezing level 800 m.

THURSDAY: Mostly sunny / Light, northwest ridgetop wind / alpine high temperature 3 / Freezing level 1500 m.

FRIDAY: Mostly sunny / Light, west ridgetop wind / alpine high temperature 3 / Freezing level 1500 m.

SATURDAY: Mostly sunny / Light, southeast ridgetop wind / alpine high temperature 2 / Freezing level 1300 m.

Avalanche Summary

No new avalanches were reported in this region on Tuesday. However, observations are very limited this time of year.

Over the weekend, there were reports of numerous large (size 2) wet loose avalanches on south-facing slopes at all elevations and a few large (size 2-2.5) cornice failures on a variety of aspects. 

One wet slab was suspected to have released on the November crust layer on a shallow west aspect in the alpine, triggered by a loose wet avalanche from above. Cornice fall, loose wet avalanches, or a rider hitting a thin spot in the snowpack should be considered if riding on steep, rocky slopes with a shallow or thin to thick snowpack as they are the most likely ways to trigger deeply buried weak layers.

Snowpack Summary

The snowpack has been undergoing a melt-freeze cycle with successive days of warm sunny weather. Strong solar radiation and warming will likely initiate wet loose avalanches as the snow loses cohesion. As the heat penetrates deeper into the snowpack, operators have reported larger wet slab avalanches. These avalanches are dense, destructive, and can run far, reaching otherwise snow-free valley bottoms. Cornices are large and looming along ridgelines. Sun and warm temperatures will increase the chances of cornice failures, especially when temperatures remain above zero overnight. Check out the Forecaster's Blog for information on how to manage these spring conditions. 

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

  • Avalanche hazard is expected to to increase througout the day, think carefully about your egress.
  • Back off slopes as the surface becomes moist or wet with rising temperatures.
  • As surface loses cohesion due to melting, loose wet avalanches become common in steeper terrain.
  • Minimize overhead exposure; avalanches triggered by warming or cornice fall may be large and destructive.

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.