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Avalanche Forecast

Archived

Apr 11th, 2021–Apr 12th, 2021

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

Regions

Lizard-Flathead.

Lingering wind slabs may remain reactive to human triggers on lee features below ridgetops at treeline and above. Expect natural wet loose avalanches to occur on solar aspects if the sun comes out.

Confidence

High -

Weather Forecast

  

SUNDAY NIGHT: Mostly cloudy with convective flurries; 5-15 cm. / Light, southeast ridgetop wind / alpine low temperature -10 / Freezing level valley bottom.

MONDAY: Mix of sun and cloud / Light, northeast ridgetop wind / alpine high temperature -1 / Freezing level 1500 m.

TUESDAY: Mostly sunny / Light, northeast ridgetop wind / alpine high temperature 0 / Freezing level 1500 m.

WEDNESDAY: Mostly sunny / Moderate, northeast ridgetop wind / alpine high temperature 1 / Freezing level 1700 m.

Avalanche Summary

Explosive triggered dry loose and slab avalanches up to size 1.5 were reported on Saturday. 

Snowpack Summary

Lingering wind slabs formed by 30-40 cm. of recent snow and previously strong southwesterly winds may remain reactive on lee features 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 is sitting on hard crusts on solar aspects and a mix of wind affected or soft surfaces on shady aspects.

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

The mid-pack is firm and well settled. Some faceted snow and a decomposing melt-freeze crust can be found near the base of the snowpack that may become a concern when the next big warm-up arrives.

Snow line is slowly creeping up the mountains to roughly 1400 m in elevation. Check out this MIN report for more details on the access from common staging areas.

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

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Avoid freshly wind loaded terrain features.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Back off slopes as the surface becomes moist or wet with rising temperatures.

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.