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Avalanche Forecast

Archived

Apr 9th, 2021–Apr 10th, 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 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.

Regions

South Coast Inland.

Ease into terrain in an assessment mindset, expecting reactivity of new snow to increase with elevation, wind effect, or sun exposure. Danger in the north of the region may be a step lower, but gather solid information (new snow depth/reactivity) before committing to your line.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Friday night: Continuing flurries bringing new snow totals in the north of the region to about 15 cm, closer to 25-30 cm in the south of the region. Strong southwest wind shifting west as snowfall eases.

Saturday: Mainly cloudy. Light to moderate northwest winds easing over the day. Alpine high temperatures around -8 with freezing levels to 1200 metres. 

Sunday: Sunny. Light variable winds. Alpine high temperatures around -3 with freezing levels to 1700 metres.

Monday: Mainly sunny. Light northeast winds. Aline high temperatures around -3 with freezing levels to 1700 metres.

Avalanche Summary

The region will likely see a north/south split in conditions for Saturday, with a more widespread and reactive storm slab problem likely to form in the south of the region and more limited new wind slab distribution in the north. Whatever accumulates locally, any solar exposure will likely cause it to shed naturally from steep, sun exposed slopes during the day.

A natural avalanche cycle was observed in the region on Saturday during the last storm. 

Snowpack Summary

5-10 cm of snow is expected to fall on Friday, bringing this week's storm snow totals to about 15-30 cm. The Coquihalla could see up to 30 cm of new snow, bringing totals there closer to 40-50 cm. Strong southwest wind is forecast for the storm, meaning thicker, touchier wind slabs are likely to form in exposed leeward terrain.

The recent storm snow sits on a crust in most areas, except on north aspects above about 1500 m where it sits on either wind slabs or soft snow.

Cornices are large and looming along ridgelines. Their release is unpredictable, requiring a large berth if you're travelling above or below them.

Terrain and Travel

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Even brief periods of direct sun could produce natural avalanches.
  • 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.