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Avalanche Forecast

Archived

Apr 5th, 2021–Apr 6th, 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.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

South Rockies.

Watch for cornices and wind slabs near ridgetops and be cautious on sun-exposed slopes.

Confidence

Moderate - Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

MONDAY NIGHT: Clear, light northwest wind, treeline temperatures below -6 C with freezing level dropping to valley bottom.

TUESDAY: Sunny, southwest wind increasing to moderate through the day, treeline temperatures reach +4 C with freezing level climbing to 2200 m.

WEDNESDAY: Increasing cloud and some light afternoon flurries, moderate to strong southwest wind, treeline temperatures reach +3 C with freezing level around 2000 m.

THURSDAY: Snow, 5-20 cm, decreasing southwesterly wind, treeline temperatures below -6 C with freezing level dropping below 1000 m.

Avalanche Summary

The last reported avalanche activity was on Thursday when some small wet loose avalanches were observed on steep sun-exposed slopes.

Snowpack Summary

Sunny alpine slopes turned moist on Monday afternoon, 5-15 recent dry snow persists at upper elevations and in shady and north-facing terrain. Some small wind slabs may be found on lee features below alpine ridgetops. Cornices are large, looming, and capable of triggering 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. 

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.
  • Carefully evaluate steep lines for wind slabs.
  • Be alert to conditions that change with elevation and sun exposure.
  • 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.