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Avalanche Forecast

Archived

Feb 20th, 2021–Feb 21st, 2021

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

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 - Forecast snowfall amounts are uncertain.

Weather Forecast

A warm front crossing the region will peak in intensity on Sunday night.

SATURDAY NIGHT: Cloudy with scattered flurries bringing 5 cm of snow, strong southwest wind, treeline temperatures around -8 C.

SUNDAY: Scattered flurries with 5-15 cm throughout the day, strong southwest wind, freezing level climbing up to 1100 m, treeline temperatures reach -4 C.

MONDAY: Heavy flurries overnight and throughout the day bring 15-25 cm of snow, strong southwest wind, freezing level around 1300 m with treeline temperatures around -2 C.

TUESDAY: Clearing skies, light to moderate west wind, treeline temperatures drop to -8 C.

Avalanche Summary

On Friday, skiers triggered several thin (size 1) storm slab and dry loose avalanches in the 15 cm of new snow. Explosive control also produced a few larger (size 2) storm slabs that were up to 50 cm thick. 

Minimal significant avalanche activity was reported between Tuesday and Thursday. 

Last weekend there were numerous wind slab avalanches on northwest, north, northeast, and east facing features, while in the first two weeks of February there were many reports of human triggered persistent slab avalanches. The persistent slab 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

With another 10-20 cm of snow expected by Sunday afternoon there could be 20-40 cm of recent snowfall to form reactive storm and wind slabs. This storm snow has buried old hard wind slabs that may still be reactive on steep high elevation slopes. The main persistent layer of concern is a combination of surface hoar, facets, and crust layers that formed in January that are now buried 60-100 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

  • Watch for fresh storm slabs building throughout the day.
  • Choose slopes that are well supported and have limited consequence.
  • Use ridges or ribs to avoid areas of wind loaded snow.
  • Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.

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.