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Avalanche Forecast

Archived

Feb 1st, 2021–Feb 2nd, 2021

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

Regions

South Coast.

The South Coast has been bit by some intense snow and rain, which is keeping danger elevated. Avoid avalanche terrain.

Confidence

Moderate - Forecast precipitation (either snow or rain) amounts are uncertain. Uncertainty is due to difficult to forecast freezing levels.

Weather Forecast

MONDAY NIGHT - Snow and rain, 20-30 cm/mm / strong southwest wind / alpine low temperature near -1 / freezing level 1200m, falling to 800 m overnight

TUESDAY - Flurries, 5-10 cm / moderate southwest wind / alpine high temperature near -2 / freezing level 700 m

WEDNESDAY - Mainly sunny / light northwest wind / alpine high temperature near -4 / freezing level 

THURSDAY - Snow, 10-15 cm / strong west wind / alpine high temperature near -4 / freezing level 500 m, rising to 1000 m in the afternoon

Avalanche Summary

Natural avalanches are expected on Tuesday, 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 South Coast mountains, with natural and/or human triggered avalanches reported every day since last Monday. These avalanches have 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 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

20-30 cm/mm of precipitation is expected for Monday night, with falling freezing levels bringing some snow back to lower elevations. Around 5-10 cm is expected on Tuesday.

There is now about 125-175 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 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

  • 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.