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Avalanche Forecast

Archived

Mar 28th, 2021–Mar 29th, 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 unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Northwest Coastal.

Recent heavy snowfall combined with strong wind means that storm slabs are widespread and are likely to be triggered by humans, especially in wind loaded areas at treeline and in the alpine.

Confidence

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

Weather Forecast

SUNDAY NIGHT - Clear with cloudy periods / moderate north wind / alpine low temperature near -10 

MONDAY - A mix of sun and cloud / moderate to strong northwest wind / alpine high temperature near -7 

TUESDAY - Cloudy with scattered flurries, 5 cm / strong west wind / alpine high temperature near -5 / freezing level 1000 m 

WEDNESDAY - Flurries, 5-10 cm / strong southwest wind / alpine high temperature near -5 / freezing level 1000 m

Avalanche Summary

Avalanche activity is expected to taper now that the storm is over, but reactive storm slabs are still expected, especially in wind loaded areas. If the sun comes out on Monday, it could quickly initiate natural avalanches.

A widespread avalanche cycle occurred during the day on Saturday with storm slabs up to size 3 and wet loose avalanches up to size 2 throughout the region. It's likely that this avalanche cycle continued into Sunday.

There was one notable size 3 explosive triggered avalanche reported near Ningunsaw on Thursday that was suspected to have failed on the mid-February persistent weak layer.

Several size 2-3 natural glide slab avalanches have been reported over the last week. Avoid slopes with glide cracks on them at all times. They are inherently unstable and can release at any time.

Snowpack Summary

30-60 cm of new snow fell in the region since Friday night, accompanied by strong southwest wind. Storm slabs are expected to be reactive at upper elevations. Much of the recent precipitation fell as rain at lower elevations. The snow surface below treeline has likely frozen into a crust in many areas.

At higher elevations, the new snow has added significant load to a couple of deeply buried weak layers that we haven't quite ruled out as problems.

The first and most concerning persistent weak layer was buried in mid-March and is around 100-180 cm deep. It consists of surface hoar on sheltered northerly aspects around treeline. 

Down between 150 to 250 cm is another layer of surface hoar and facets, buried in mid-February. This layer may still be a concern in shallower snowpack areas. 

The mid and lower snowpack is well settled and strong in most areas.

Terrain and Travel

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Keep in mind that human triggering potential persists as natural avalanching tapers off.
  • 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.