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Avalanche Forecast

Archived

Feb 22nd, 2021–Feb 23rd, 2021

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

Regions

Kootenay Boundary.

Human triggered avalanches are possible at all elevations, watch for signs of instability and gather information before exposing yourself to avalanche terrain.

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

A few days of cool dry weather.

MONDAY NIGHT: Scattered flurries with 5-10 cm of snow, strong west wind at ridgetops, treeline temperatures drop to -10 C.

TUESDAY: Mix of sun and cloud, light wind with some moderate gusts from the west, treeline temperatures around -8 C.

WEDNESDAY: Sunny, light wind, treeline temperatures around -8 C.

THURSDAY: Scattered flurries with 5-10 cm of snow, moderate southwest wind, treeline temperatures around -8 C.

Avalanche Summary

Steady pulses of snow between Wednesday and Saturday resulted in surprisingly little avalanche activity, but by Sunday there were several reports of size 1-1.5 storm and wind slab avalanches. These avalanches were mostly 20-30 cm thick and were triggered both naturally and by humans. Explosive control produced a few larger (size 2) avalanches.

There were many reports of human triggered persistent slab avalanches during the first two weeks of February. These avalanches failed on a surface hoar layer that is now 50-100 cm deep and is most prevalent at treeline elevations. There were also two very large explosive triggered avalanches in the Bonningtons in the past month that stepped down to the early December crust (most recently on Feb 9). These deeper instabilities have been trending towards being unreactive, however occasional snowpack tests suggest they may still be possible to trigger in some areas.

Snowpack Summary

25-50 cm of recent snow is likely heavily wind affected in open terrain while in sheltered terrain it could either be low density powder or heavy and slabby. The main persistent layer of concern is a combination of surface hoar, facet, and crust layers that formed in January that are now buried 50-100 cm deep. An early season crust near the bottom of the snowpack has periodically produced avalanches in thinner snowpack areas. These persistent layers have appeared to gone dormant in the past week, but steep open slopes should still be assessed carefully.

Terrain and Travel

  • Be careful as you transition into wind affected terrain.
  • Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.
  • If you are increasing your exposure to avalanche terrain, do it gradually as you gather information.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.

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.