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Avalanche Forecast

Archived

Feb 1st, 2021–Feb 2nd, 2021

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

Regions

Kootenay Boundary.

Expect to see reactive storm slab conditions, especially in wind loaded areas. Choose conservative terrain and avoid overhead hazard.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

MONDAY NIGHT - Flurries, 10-15 cm / strong southwest wind / alpine low temperature near -4 / freezing level 1600 m

TUESDAY - Flurries, 5 cm / moderate to strong southwest wind / alpine high temperature near -5 / freezing level 1500 m, dropping to valley bottom overnight

WEDNESDAY - A mix of sun and cloud / light northwest wind / alpine high temperature near -10 

THURSDAY - Mainly cloudy with a few flurries / moderate west wind / alpine high temperature near -9

Avalanche Summary

Human triggered avalanches are expected to be easy to trigger on Tuesday, especially in wind loaded areas.

At the time of publishing, there were a few reports of size 1.5-2 explosives triggered storm slab avalanches in the region on Monday.

There were numerous size 1-1.5 human and explosives triggered avalanches reported on Sunday. Several of these were reported to have failed on the recently buried persistent weak layer.

On Thursday and Friday, there were numerous reports of size 1-2 human triggered avalanches. These avalanches failed on the persistent weak layer of surface hoar that was buried in late January.

Snowpack Summary

10-15 cm of snow is expected on Monday night, with another 5 cm on Tuesday.

There is now about 50-70 cm of recent storm snow sitting above a persistent weak layer that consists of a melt-freeze crust in many areas, on a sun crust on steep south-facing slopes, and large surface hoar in sheltered areas.

There are potentially several more layers of surface hoar in the upper snowpack, with the most notable one down about 60-120 cm. This layer was buried in early January. 

A couple of crusts surrounded by weak faceted grains are buried deep within the snowpack. The upper layer is 150 to 200 cm deep and the lower one is near the ground. 

Terrain and Travel

  • Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.

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.