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Avalanche Forecast

Archived

Mar 21st, 2021–Mar 22nd, 2021

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

Don't let the new snow lure you into consequential avalanche terrain, human triggered avalanches will be likely on Monday.

Confidence

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

Weather Forecast

A cool northwest flow starts in the wake of the Sunday night storm.

SUNDAY NIGHT: 15-20 cm of snow overnight at the trailing end of the storm, 40-50 km/h south wind, freezing level around 1000 m with treeline temperatures around -2 C. 

MONDAY: Mostly sunny with some brief flurries, 20-30 km/h northwest wind, freezing level drops to 600 m with treeline temperatures around -2 C.

TUESDAY: Mix of sun and cloud, 20-30 km/h west wind, treeline temperatures around -3 C.

WEDNESDAY: Cloudy with scattered flurries bringing 10-15 cm of snow, 30-50 km/h southwest wind, freezing level climbing to 1200 m with treeline temperatures around -1 C.

Avalanche Summary

Storm slabs will grow rapidly on Sunday night with some natural activity likely during the peak of the storm in the evening. See this MIN report that shows storm slab reactivity increasing during the day on Sunday.

These slabs will gradually strengthen throughout the day on Monday, but human triggered slabs are still a concern and it will be important to carefully monitor the reactivity of storm snow through the day.

Snowpack Summary

As the storm eases on Monday morning there will be 30-50 cm of fresh storm snow. Amounts will likely increase dramatically with elevation. The snow is should strengthen relatively quickly when storm ends, but storm slabs will still be a concern throughout the day. North facing slopes likely have thicker slabs due to wind loading. 

Along ridgelines, cornices are large and always have the potential of failing or being triggered from the weight of a human.

Terrain and Travel

  • Don't be too cavalier with decision making, storm slabs may remain sensitive to human triggering.
  • If you are increasing your exposure to avalanche terrain, do it gradually as you gather information.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • Use caution above cliffs and terrain traps where even small avalanches may have severe consequences.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

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.