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Avalanche Forecast

Archived

Feb 19th, 2022–Feb 20th, 2022

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 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.

Regions

Kootenay Boundary.

Keep terrain selection conservative as storm snow accumulates on Sunday. Avoid avalanche terrain and overhead hazard during heavy snowfall.

Small avalanches may step down to deeper instabilities, most likely on sheltered north facing slopes.

Confidence

Moderate - We are confident the likelihood of avalanche will increase with the arrival of the forecast weather. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

SATURDAY NIGHT: 5-10cm of snow possible overnight, heaviest in the east near Nelson. Light westerly winds. Freezing level around 1200 m dropping to valley bottom.

SUNDAY: Mostly cloudy with snowfall continuing over the day. 10-20 cm is forecast, again heaviest near Nelson. Light northwest winds. Freezing levels around 1200 m. Alpine high of -6.

MONDAY: Mix of sun and cloud, light winds from the north. Chance of isolated flurries. Freezing levels at valley bottom. Alpine high of -10. 

TUESDAY: Mostly clear skies with moderate northeast winds. Freezing levels at valley bottom, alpine high of -12. 

Avalanche Summary

There have been regular reports of small natural and human-triggered wind slabs along ridgetops over the past few days. With the incoming storm we expect to see larger slabs forming at upper elevations. 

Persistent slab avalanches were reported on Friday from explosive and human triggers, failing on the late January surface hoar layer. This activity was limited to north/northeast aspects around tree line elevations - these specific areas continue to be a concern for human triggering throughout this storm. 

Snowpack Summary

New snow will form reactive storm slabs at all elevations. The storm snow will bury a small surface hoar layer in sheltered terrain - which sits over a melt freeze crust on solar aspects at all elevations, and wind effected surfaces in exposed terrain. 

Two layers of buried surface hoar sit in the upper snowpack, most likely to be found and triggered on north aspects in sheltered areas. These are now down around 30-50 cm and 60-80 cm deep. These layers remain reactive in some snowpack tests and have resulted in avalanche activity over the past week. 

The lower snowpack is well consolidated, with a crust/facet layer found 100 to 200 cm deep. It is currently considered dormant, but could become active later this season. Check out the forecaster blog for more information. 

Terrain and Travel

  • Use increased caution at all elevations. Storm snow is forming touchy slabs.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Avoid all avalanche terrain during periods of heavy snowfall.

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.