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Avalanche Forecast

Archived

Feb 21st, 2021–Feb 22nd, 2021

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

Regions

Kootenay Boundary.

Avoid wind loaded slopes and pay close attention to changing conditions throughout the day as avalanche danger will increase throughout the storm.

 

Confidence

Moderate - Uncertainty is due to how the snowpack will react to the forecast weather.

Weather Forecast

A warm front crossing the region Monday will bring 15-25 cm of snow with mild temperatures and strong wind.

SUNDAY NIGHT: Cloudy with scattered flurries bringing 5-10 cm of snow, strong southwest wind, freezing level climbing to 1200 m with treeline temperatures around -4 C.

MONDAY: Cloudy with scattered flurries and another 5-15 cm of snow, strong west wind, freezing level around 1300 m with treeline temperatures around -2 C.

TUESDAY: Mix of sun and cloud, light wind, treeline temperatures drop to -8 C.

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

Avalanche Summary

Steady pulses of snow since Wednesday have resulted in surprisingly little avalanche activity. On Friday and Saturday there were some small dry loose avalanches and some small (size 1) skier triggered snow slab avalanches. Explosive control on Friday produced a few larger (size 2) slabs on bigger terrain features that were up to 50 cm thick. 

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 have also been 2 very large explosive triggered avalanches in the Bonningtons in the past month (most recently on Feb 9) that stepped down to the early December crust to produce a 200 cm deep, size 3.5 avalanche.

Snowpack Summary

It has been snowing steadily for several days, but no single pulse big enough to form reactive storm slabs. The final pulse on Monday could bring recent storm totals to 30-50 cm, which may be enough for storm slab formation to be a serious concern. The main persistent layer of concern is a combination of surface hoar, facets, 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 could re-emerge as a problem with the incoming weather.

Terrain and Travel

  • Travel in alpine terrain is not recommended.
  • Avoid freshly wind loaded terrain features.
  • Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.
  • Watch for fresh storm slabs building throughout the day.
  • Choose slopes that are well supported and have limited consequence.

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.