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Avalanche Forecast

Archived

Dec 21st, 2020–Dec 22nd, 2020

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.
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.

Snow, rain, and wind will hammer the region Monday night. Buried weak layers will need time to equilibrate to this substantial load. Travel in avalanche terrain is not recommended until we have evidence of a stabilizing snowpack.

Confidence

Moderate - Forecast precipitation (either snow or rain) amounts are uncertain.

Weather Forecast

MONDAY NIGHT: Snow, accumulation 20 to 40 cm with the most in the west of the region, 40 to 80 km/h west wind, alpine temperature -1 C, freezing level 1800 m.

TUESDAY: Mix of sun and cloud, 40 km/h north wind, alpine temperature -10 C.

WEDNESDAY: Clear skies, 10 to 20 km/h west wind, alpine temperature -8 C.

THURSDAY: Clear skies, 20 km/h southwest wind, alpine temperature -2 C.

Avalanche Summary

It is anticipated that a natural avalanche cycle occurred during the storm on Monday night. Photos in this MIN show a close-up of how dangerous the snowpack is right now. Expect human-triggered avalanches to be very likely to occur on Tuesday as the snowpack equilibrates to the new load.

Snowpack Summary

A hefty storm impacted the region Monday and Monday night, with around 30 to 40 cm of snow accumulation expected by Tuesday morning. Some of the snow may fall as rain below 1800 m. Strong wind during the storm started from the south, shifted to the west, and finally to the north. Expect to find reactive storm and wind slabs across the region. The snow will likely take a few days to bond to the snowpack.

This snow is loading weak layers around 50 to 100 cm deep. The layers may be composed of feathery surface hoar and/or sugary faceted grains and they overly a hard melt-freeze crust. There has already been substantial avalanche activity on this layer from natural and human triggers. This layer remains a major concern, as humans may be able to trigger large and destructive avalanches on it.

Another crust with associated faceted grains may be found near the base of the snowpack. There have been no recent avalanches reported on this layer but it remains on our radar. The most likely place to trigger it would be from shallow, rocky terrain. 

Terrain and Travel

  • Travel in alpine terrain is not recommended.
  • Be careful to keep storm day fever from luring you out into bigger terrain features.
  • Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.

Problems

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.

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.