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Avalanche Forecast

Archived

Feb 4th, 2021–Feb 5th, 2021

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

Regions

South Coast.

Wind slabs may be found on a variety of aspects and will likely remain sensitive to human triggers Friday.

The persistent weak layer may still be possible to trigger in areas that have not already avalanched. Be especially cautious in these places.

Confidence

Moderate -

Weather Forecast

Thursday night: Mainly cloudy with a few flurries, up to 5 cm, moderate westerly ridgetop wind, treeline temperature -5, freezing level 700 m.

Friday: Mix of sun and cloud, light northwest ridgetop wind, treeline high -1, freezing level 1000 m.

Saturday: Light flurries, up to 5 cm, strong northwest ridgetop wind, treeline high -1, freezing level 1000 m. 

Sunday: Mix of sun and cloud, light westerly ridgetop wind, treeline high -1, freezing level 500 m. 

Avalanche Summary

Human triggered storm slab avalanches remain likely in wind loaded areas at upper elevations. The recently buried persistent weak layer may be possible to trigger in areas that have not already avalanched.

It was a busy week for avalanche activity in the South Coast mountains, with natural and/or human triggered avalanches reported every day between Monday, January 25, and Monday, February 1, culminating in a widespread natural avalanche cycle, with avalanches up to size 3, on Monday night. Most of these avalanches failed on the persistent weak layer. This was likely the peak of the avalanche activity associated with this layer. 

North Shore Rescue responded to a serious, but non-fatal avalanche incident last Tuesday evening near Cypress Mountain Resort. One person was involved and was partially buried. The avalanche was a size 2 storm slab on a west aspect at approximately 1100 m and failed on the persistent weak layer.

Snowpack Summary

80-150 cm of snow sits over a widespread persistent weak layer. This weak layer consists of a crust that also has weak facets and surface hoar on top of it in many areas. This layer has been taking more time to gain strength than what is considered typical for the South Coast region.

Click here to watch North Shore Rescue's January 29 snowpack discussion, which illustrates this concerning snowpack structure.

Terrain and Travel

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Avoid freshly wind loaded terrain features.
  • Be aware of highly variable recent wind loading patterns.
  • Be aware of the potential for large avalanches due to the presence of buried weak layers.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.