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Avalanche Forecast

Archived

Feb 3rd, 2021–Feb 4th, 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, 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.

Regions

South Coast.

Wind loading is expected on southerly slopes from strong northwest wind, which is not the typical pattern for the region.

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 - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

WEDNESDAY NIGHT - Mainly cloudy / moderate northwest wind / alpine low temperature near -3 / freezing level 700 m

THURSDAY - Mainly cloudy with a few flurries, 3-5 cm / moderate to strong northwest wind / alpine high temperature near -2 / freezing level 600 m

FRIDAY - Mainly cloudy / strong northwest wind, easing to moderate in the afternoon / alpine high temperature near -1 / freezing level 1000 m 

SATURDAY - Mainly cloudy with scattered flurries, 3-5 cm / strong west wind / alpine high temperature near -2 / freezing level 900 m

Avalanche Summary

Human triggered 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.

A widespread natural avalanche cycle, with avalanches up to size 3, took place on Monday night. Most of these avalanches failed on the persistent weak layer. This was likely the peak of the avalanche activity in the region. 

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. Most of these avalanches failed on the persistent weak layer that was recently buried. 

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

There is about 80-150 cm of snow sitting on 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

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

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.