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Avalanche Forecast

Archived

Apr 6th, 2021–Apr 7th, 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 unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Lizard-Flathead.

Watch for cornices and reactive slabs in wind-drifted areas near ridgetops. 

Confidence

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

Weather Forecast

Tuesday night: Clear, moderate southwest wind, treeline temperatures near 0 C, freezing level staying elevated at 2000 m.

Wednesday: Increasing cloud, isolated light afternoon flurries with trace accumulations, moderate southwest wind, treeline temperatures near -1 C, freezing level dropping from 1800 m to valley bottom.

Thursday: Mainly cloudy, 5-15 cm of snow, light west wind, treeline temperatures near -7 C, freezing level rising to 1500 m and dropping to valley bottom.

Friday: Increasing cloud, isolated flurries with trace accumulations, light southwest wind, treeline temperatures near -2 C, freezing level rising to 1600 m and dropping to valley bottom.

Avalanche Summary

On Monday and Tuesday, pinwheels and small loose wet avalanches were observed on steep sunny alpine slopes.

Snowpack Summary

Small wind slabs may be found on lee features below alpine ridgetops. Cornices are large, looming, and capable of triggering avalanches when they fail.

Sunny alpine slopes likely became moist on Tuesday afternoon. 5-15 cm of recent dry snow persists at upper elevations in shady north-facing terrain. Check out this MIN report for a helpful photo and description of the conditions from Mongolia Ridge.

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. 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

  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Watch for wind-loaded pockets especially around ridgecrest and in extreme terrain.
  • Carefully evaluate steep lines for wind slabs.

Problems

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.

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.