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

Regions

Kootenay Boundary.

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 - Forecast snowfall amounts are uncertain.

Weather Forecast

SUNDAY NIGHT - Flurries, 10-15 cm / strong southwest wind / alpine low temperature near -5 / freezing level 1500 m

MONDAY - Flurries, 10-15 cm with another 15-20 cm overnight / moderate to strong southwest wind / alpine high temperature near -4 / freezing level 1500 m

TUESDAY - Flurries, 5 cm / moderate to strong southwest wind / alpine high temperature near -7 / freezing level 1500 m and dropping to valley bottom overnight

WEDNESDAY - Mainly cloudy / light west wind / alpine high temperature near -10

Avalanche Summary

Natural and human triggered avalanches are expected to be likely on Monday with continued stormy weather creating reactive storm slabs.

On Thursday and Friday, there were numerous reports of size 1-2 human triggered storm slab avalanches. The primary failure plan in these avalanches was the latest weak layer of surface hoar from late January that was 20-40 cm deep at the time.

Snowpack Summary

Fresh snow accumulations between Sunday night and Monday afternoon are expected to be around 20-30 cm. There is now about 60-80 cm of total recent storm snow sitting above a melt-freeze crust in many areas around treeline and below treeline, on a sun crust on steep south-facing slopes, and on 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 100 to 150 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.
  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • 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.