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Avalanche Forecast

Archived

Mar 22nd, 2022–Mar 23rd, 2022

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

Regions

Northwest Coastal.

Take a conservative approach in the wake of the storm. Storm slabs are primed for human triggering.

Confidence

High -

Weather Forecast

Tuesday night: Snowfall 5-15 cm. Moderate southwest wind. Alpine low around -8 °C. Freezing level dropping to 500 m. 

Wednesday: Flurries around 5 cm. Moderate southwest wind. Alpine high around -6 °C. Freezing level 1000 m. 

Thursday: A mix of sun and cloud. Moderate southeast wind. Alpine high around -5 °C. Freezing level 1200 m.

Friday: A mix of sun and cloud. Moderate south wind. Alpine high around -5 °C. Freezing level 1200 m.

Avalanche Summary

Observations during the storm have been limited by visibility. Preliminary reports include size 1-2 loose wet avalanches observed near valley bottom. We expect a large, widespread storm slab avalanche cycle to have occurred, including step-downs to the persistent layer.

Prior to the storm, reports of persistent slab avalanches were steadily coming in over the last week from northwest of Terrace. These avalanches were large to very large (size 2-3), failing on a weak layer buried 60-100 cm deep mostly on northeast facing slopes. These avalanches were easily triggered by riders and vehicles, some remotely or sympathetically, and propagating long distances.

Snowpack Summary

30-50 cm of heavy new snow has been distributed by strong southwest wind at upper elevations. Below 1500 m, new snow depths taper and the snow may sit over a wet or crusty upper snowpack.

A weak layer of surface hoar is now buried 100-150 cm deep. A thick rain crust from mid-February 130-200 cm deep caps a well consolidated lower snowpack.

Terrain and Travel

  • Keep in mind that human triggering potential persists as natural avalanching tapers off.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Avoid freshly wind loaded terrain features.
  • If triggered, storm slabs in-motion may step down to deeper layers and result in very large 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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.