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Avalanche Forecast

Archived

Jan 31st, 2021–Feb 1st, 2021

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

Regions

South Coast.

Continued stormy weather is keeping danger elevated as more snow adds load to a buried weak layer. Stick to simple terrain with no overhead hazard.

Confidence

Moderate - We are confident about the likelihood of avalanche activity, what is less certain are their possible size.

Weather Forecast

SUNDAY NIGHT - Snow mixed with rain, 5 cm/mm / moderate to strong southwest wind / alpine low temperature near 0 / freezing level 1200 m

MONDAY - Snow mixed with rain, 15-25 cm/mm, with another 25 cm/mm overnight / moderate to strong southwest wind / alpine high temperature near 0 / freezing level 1500 m

TUESDAY - Snow, 10-15 cm, with another 10-20 cm overnight / moderate to strong southwest wind / alpine high temperature near -1 / freezing level 800 m and dropping to 500 m overnight

WEDNESDAY - A mix of sun and cloud / light northwest wind, picking up to moderate west wind in the afternoon / alpine high temperature near -2 / freezing level 500 m

Avalanche Summary

Natural avalanches are expected on Monday, and due to the presence of a persistent weak layer, they could be very large.

It has been a busy week for avalanche activity in the North Shore mountains, with human triggered avalanches reported everyday since Monday. These avalanches have failed on a prominent weak layer that was 30-60 cm deep at the time, and will be 60-100 cm deep by Sunday. Recent MIN reports show good examples of these avalanches (e.g. here, here, and here). 

North Shore Rescue responded to a serious, but non-fatal avalanche incident on Tuesday evening on Cypress Mountain. 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 recently buried weak layer.

Snowpack Summary

Weekend snowfall totals reached about 40-50 cm by Sunday afternoon, and there is another 15-25 cm in the forecast for Monday. At lower elevations, much of this precipitation fell as rain.

With all of this new snow, there will be about 75-115 cm of snow sitting on a widespread crust by Monday afternoon. This crust also has weak facets and surface hoar on top of it in many areas. This widespread weak layer will probably take 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 all avalanche terrain during periods of heavy snowfall.
  • Only the most simple non-avalanche terrain free of overhead hazard is appropriate at this time.
  • 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.