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Avalanche Forecast

Archived

Apr 1st, 2022–Apr 2nd, 2022

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

Regions

North Rockies.

Fresh wind slabs may be reactive to human triggering at upper elevations, especially where they sit above a crust. 

Confidence

Moderate - Forecast precipitation (either snow or rain) amounts are uncertain.

Weather Forecast

Unsettled weather is forecast for the weekend. This will bring mostly cloudy skies, new snow of 5-10 cm, and moderate to strong southwest winds at ridgetop. Freezing levels will rise to 1500 m during the day and drop overnight. 

Avalanche Summary

No new avalanches were reported on Thursday.

On Wednesday in the Renshaw area, several natural wind slab avalanches were reported and machine-triggered slabs up to size 1.

Snowpack Summary

Above 2000 m, 10-20 cm of new snow overlies 20 cm of denser snow that tapers rapidly with elevation. Below 2000 m a melt-freeze crust exists on all aspects and to mountain top on solar aspects. Below the crust, the top 10-30 cm of the snowpack is moist. This brings 50-60 cm over the mid-March interface at upper elevations. 

Westerly winds have formed reactive wind slabs on leeward terrain in the alpine and exposed treeline terrain.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Wind slabs may be poorly bonded to the underlying crust.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.

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.