Dashboard Regions Weather Stations Radar Alerts Glossary
Contact About
Log In

Register for an account and never miss a forecast again!

Register

Avalanche Forecast

Archived

Dec 21st, 2021–Dec 22nd, 2021

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

Another winter storm with strong winds and heavy snowfall will build fresh and reactive storm slabs through the forecast period.

Confidence

Moderate - Uncertainty is due to the timing, track, & intensity of the incoming weather system.

Weather Forecast

Expect some enhanced snowfall amounts Wednesday through Thursday as a warm and wet air mass rises from the South and collides with a predominantly colder air mass sliding down from the North.

Tuesday Night: New snow up to 10 cm accompanied by moderate ridgetop wind from the SW. Alpine temperatures near -8 and freezing levels at the valley bottom.

Wednesday: New snow throughout the day, heavy at times with 10-25 cm of accumulation. Strong to extreme ridgetop wind and alpine temperatures near -8. Freezing levels 1000 m.

Thursday: New snow 10-25 cm accompanied by strong SW winds. Alpine temperatures near -5 and freezing levels steady at 1000 m.

Friday: Mostly cloudy with 10 cm of new snow. Gusty ridgetop winds from the South and freezing levels dropping back to the valley bottom. 

Avalanche Summary

On Monday, several natural wind slabs and dry loose avalanches were seen up to size 2. 

With another winter storm on the horizon, natural storm slab avalanches will be likely through the forecast period. 

Snowpack Summary

New snow and wind will likely build reactive storm slabs through Friday. This new snow will bury older wind slabs from last weekend's storm and existing surface hoar that has been reported throughout the Kootenay Pass and Nelson area. 

Below the new snow 50 to 80 cm of a well-consolidated upper snowpack overlies a substantial crust that formed in early December. This crust is approximately 10 cm thick on average and is present across all aspects to at least 2300m. A layer of weak facets (sugary snow) has been reported above this crust. This problem is particularly hard to predict and tricky to manage. For this reason, wide, conservative terrain margins and disciplined backcountry travel techniques will be very important. Get more details and photos in our forecaster blog. 

The lower snowpack is composed of several early-season crusts. Snow depths at treeline average 150-200 cm. Below 1800 m the snowpack remains relatively shallow with 80-120 cm on average. The deepest snowpack can be found in the Kootenay Pass area.

Terrain and Travel

  • 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 persistent weak layers.
  • Watch for fresh storm slabs building throughout the day.

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.