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Avalanche Forecast

Archived

Dec 31st, 2022–Jan 1st, 2023

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 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.

Regions

Kootenay Boundary, Bonnington, Grohman, Kootenay Pass, Norns, Rossland, South Okanagan, Ymir, Moyie, St. Mary.

Triggering large persistent slab avalanches is a serious concern this weekend. Conservative terrain choices are strongly recommended.

Confidence

Moderate

Avalanche Summary

A natural avalanche cycle occurred between December 26 and 28th that included large and very large (size 2 to 3) storm slab and persistent slab avalanches. While natural avalanche activity has slowed down, we continue to see notable human triggered avalanches.

There were multiple remotely triggered size 2 and 3 persistent slab avalanches in Bonnington and Kokanee areas on Thursday. These occurred on north and east facing slopes between the elevations of 1800 and 2200 m. Although just outside the boundary of this forecast, the photos in this MIN report illustrate the type of terrain where these avalanches are occurring. The failure layers were typically 60 to 80 cm deep and included both of the persistent weak layers discussed in the Snowpack Summary.

Looking ahead, triggering large persistent slab avalanches remains a serious possibility.

Snowpack Summary

Around 30 to 40 cm of snow overlies a melt-freeze crust that extends up to 2000 m. Moist snow or a surface crust may be found below treeline.

Buried weak layers continue to show signs of instability. The two prominent layers of concern are a 60 to 80 cm deep layer of surface hoar and a crust on south aspects that was buried in mid-December and an 80 to 150 cm deep layer of surface hoar and facets that was buried in mid-November. Both of these layers have been most reactive between 1800 and 2200 m.

Weather Summary

Saturday Night

Cloudy with trace precipitation, 10 to 20 km/h west wind, treeline temperature -7 °C.

Sunday

Mix of sun and cloud with no precipitation, 10 km/h northwest wind, treeline temperature -5 °C, freezing level 1000 m.

Monday

Mix of sun and cloud with no precipitation, 20 km/h south wind, treeline temperature -5 °C.

Tuesday

Sunny with no precipitation, 10 km/h southwest wind, treeline temperature -5 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Choose conservative terrain and watch for clues of instability.
  • Be mindful that deep instabilities are still present and have produced recent large avalanches.
  • Remote triggering is a concern, avoid terrain where triggering slopes from below is possible
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.

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.