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Avalanche Forecast

Archived

Mar 29th, 2021–Mar 30th, 2021

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

Regions

Northwest Coastal.

 Recent snowfall combined with strong wind has built fresh wind slabs on leeward slopes 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

Another Pacific frontal system is due to arrive Wednesday bringing snow at upper elevations and strong wind. 

Tuesday: Cloudy with isolated flurries. Ridgetop wind strong from the southwest. Freezing levels 1000 m.

Wednesday: Snow 5-15 cm. Ridgetop wind strong from the South. Alpine temperatures near -3 and freezing levels 600 m. 

Thursday: Snow 10-20 cm. Ridgetop wind strong from the southewest and freezing levels 600 m.

Avalanche Summary

On Tuesday, several natural and explosive triggered wind slab avalanches occurred up to size 2. 

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

There was one notable size 3 explosive triggered avalanche reported near Ningunsaw last 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 over the weekend. This was accompanied by strong southwest then northwest wind. Wind slabs may continue to be reactive at upper elevations on leeward slopes. Much of the recent precipitation fell as rain at lower elevations and 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. The first 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 and down between 150 to 250 cm is another layer of surface hoar and facets, buried in mid-February. At this time these layers linger in the snowpack and remain on our radar. Skier or rider triggering a persistent weak layer may have a lower likelihood, however; if triggered the consequence would be high. 

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

Terrain and Travel

  • 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.
  • Keep in mind that human triggering potential persists as natural avalanching tapers off.
  • Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.

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.