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Avalanche Forecast

Archived

Mar 22nd, 2021–Mar 23rd, 2021

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

Regions

South Coast.

Carefully evaluate steep slopes where recent snow could still produce avalanches, especially in wind affected terrain.

Confidence

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

Weather Forecast

MONDAY NIGHT: Clear skies, light northwest wind, freezing level around 1000 m with treeline temperatures drop to -5 C. 

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

WEDNESDAY: Cloudy with scattered flurries bringing roughly 20 cm of snow throughout the day, 30-50 km/h southwest wind, freezing level climbs to 1000 m with treeline temperatures around -1 C.

THURSDAY: Mostly sunny, light northeast wind, freezing level climbing to 1300 m with treeline temperatures near 0 C.

Avalanche Summary

Widespread storm slab avalanche activity was reported on Sunday, and preliminary reports from Monday suggest they were still reactive to human triggering. On Sunday numerous size 1-2 natural slab avalanches were observed in the North Shore mountains. These avalanches were mostly 20-30 cm thick and ran on a crust layer. On Monday there were some reports of size 1.5-2 human triggered avalanches in the Seymour backcountry (30-60 cm thick). See the photos here and here. These slabs should be less reactive by Tuesday, but may still be possible to trigger in steep terrain.

Snowpack Summary

35-45 cm of snow from Sunday is settling and strengthening, but could still be unstable on some steep and wind affected slopes. Reports suggest the new snow was poorly bonded to a crust on Sunday, but this should improve quickly. Along ridgelines, cornices are large and always have the potential of failing or being triggered from the weight of a human.

Terrain and Travel

  • Exercise caution on steep, unsupported slopes.
  • Be careful as you transition into wind affected terrain.
  • 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.