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Avalanche Forecast

Archived

Apr 5th, 2021–Apr 6th, 2021

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

Regions

Northwest Coastal.

Watch for fresh slabs developing as snow and flurries accumulate through Tuesday.

Confidence

Moderate - Uncertainty is due to the track & intensity of the incoming weather system.

Weather Forecast

MONDAY NIGHT: Flurries and snow 5-10 cm, moderate west wind, treeline temperatures around -3 C with freezing levels dropping below 500 m.

TUESDAY: Ongoing flurries with up to 25 cm accumulating by the end of Tuesday, moderate southwest wind, treeline temperatures around -2 C and freezing level up to 1000 m.

WEDNESDAY: Overnight flurries tapering by morning for mix of sun and cloud, moderate west wind, treeline temperatures around -2 C and freezing level up to 1000 m.

THURSDAY: Flurries arriving late in the day, increasing southwesterly wind, treeline temperatures below 0 C with freezing level dropping below 500 m.

Avalanche Summary

Explosives successfully targeted a few glide slabs on Sunday and loose wet avalanches were observed on sunny slopes. And further inland strong winds contributed to intense wind-loading in areas with fresh wind slab avalanches to size 2 failing in immediate lee features.

During the storm on Friday and Saturday there were numerous reports of natural storm slab avalanches at upper elevations (up to size 2), as well as many loose wet avalanches on steep sun-exposed slopes on Saturday afternoon.

Over the past few week there have been some large natural and explosive triggered glide slab avalanches along the Skeena corridor. Glide cracks releasing as full depth glide slab avalanches are extremely difficult to predict. Best practice is to avoid slopes with glide cracks.

Snowpack Summary

Over the past week, 40-60 cm of snow has fallen at upper elevations. While this snow is well settled, wind slabs may linger on steep open slopes. Sun crusts may be found on sun-exposed slopes. Cornices are large, looming, and capable of triggering large avalanches when they fail. Previous weak layers are now deeply buried and have not resulted in any recent avalanches.

At lower elevations, recent snow was mixed with rain, soaking the snow surface, which then formed a hard crust. 

Terrain and Travel

  • Watch for changing conditions today, storm slabs may become increasingly reactive.
  • Dial back your terrain choices if you are seeing more than 25cm of new snow.
  • Carefully evaluate steep lines for wind slabs.
  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • Avoid exposure to slopes that have cornices overhead.

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.