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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 possible, human triggered probable.
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

South Rockies.

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 1800 m.

Wednesday: Increasing cloud, isolated light afternoon flurries with trace accumulations, strong southwest wind, treeline temperatures rising to 3 C, freezing level rising to 2200 m and dropping to valley bottom.

Thursday: Mainly cloudy, 10-20 cm of snow, light west wind, treeline temperatures near -5 C, freezing level rising to 1500 m and dropping to valley bottom.

Friday: Mainly sunny, moderate southwest wind, treeline temperatures near-2 C, freezing level rising to 1800 m and dropping to valley bottom.

Avalanche Summary

On Monday and Tuesday, small wet loose avalanches were observed on steep sun-exposed 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 become moist on Tuesday with strong sun and warm temperatures. 5-15 cm of recent dry snow can still be found at upper elevations in shady north-facing terrain. 

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 gradually creeping up to higher elevations.

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

  • Carefully evaluate steep lines for wind slabs.
  • Back off slopes as the surface becomes moist or wet with rising temperatures.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

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.