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Avalanche Forecast

Archived

Mar 28th, 2021–Mar 29th, 2021

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

Regions

South Coast.

Recent new snow with strong wind has formed storm slabs that are likely still reactive at upper elevations, especially in wind loaded areas.

Keep in mind that the sun can quickly initiate natural avalanche activity and weaken cornices, especially at this time of the year.

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

SUNDAY NIGHT - Cloudy with clear periods / moderate northwest wind / alpine low temperature near -4 

MONDAY - Sunny / moderate to strong north wind / alpine high temperature near -2 / freezing level 1000 m

TUESDAY - Mainly cloudy / moderate northwest wind / alpine high temperature near -4 / freezing level 1000 m

WEDNESDAY - A mix of sun and cloud / moderate west wind / alpine high temperature near 5 / freezing level 2300 m

Avalanche Summary

Avalanche activity is expected to decrease on Monday, however reactive storm slabs are still anticipated, particularly in wind loaded areas at higher elevations. Cornices are large and should be given a wide berth, especially when the sun comes out.

A natural avalanche cycle likely occurred during the day on Sunday. 

Snowpack Summary

A mix of rain and snow brought 30-50 cm/mm of precipitation to the region since Saturday night, accompanied by moderate to strong southerly winds. This precipitation fell on about 30-50 cm of older snow that fell last week. 

Rain at lower elevations has likely soaked the snowpack, which is expected to freeze into a crust with falling temperatures. 

Along ridgelines, cornices are large and may weaken when the sun comes out on Monday.

Terrain and Travel

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Be aware of highly variable recent wind loading patterns.
  • Brief periods of sun could quickly initiate natural avalanche activity.
  • Cornices become weak with daytime heating or solar exposure.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.