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Avalanche Forecast

Archived

Dec 29th, 2019–Dec 30th, 2019

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

Although the likelihood of triggering large avalanches is decreasing, the persistent slab problem warrants avoiding steep convexities and areas with a shallow, rocky, or variable snowpack.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

Sunday night: Clear, light variable winds, alpine temperatures around -10 C.

Monday: Mostly clear, light southwest winds, alpine high temperatures around -3 C with freezing levels near 700 m.

Tuesday: Mostly cloudy, 5-10 cm of snow, moderate southwest winds, alpine high temperatures near -5 C with freezing levels around 700 m.

Wednesday: Mostly cloudy, 5-10 cm of snow, light to moderate west winds, alpine high temperatures near-3 C with freezing levels around 900 m. 

Avalanche Summary

Snowpack Summary

15-20 cm of new snow fell over the weekend on a weak interface. Forecast winds did not materialize to form reactive wind slabs except in isolated areas at upper elevations. 

Last week's storm deposited 70 to 100 cm of snow and a significant load to multiple weak layers. These layers include a feathery surface hoar layer (down 70 to 110 cm), an older surface hoar layer with a melt-freeze crust on steep south aspects (down 90 to 130 cm), and a layer of sugary faceted snow, surface hoar, and melt-freeze crusts from late November found in the bottom half of the snowpack. Snowpack tests continue to produce sudden results on these layers (check out this MIN report from Friday).

Although signs of instability are becoming less obvious, it remains prudent to make terrain decisions with the understanding that one or more of these deeply buried layers are present and could produce large and destructive avalanches with human triggers.

Terrain and Travel

  • Avoid shallow snowpack areas, rock outcroppings and steep convex terrain where triggering is most likely.
  • Persistent slabs have potential to pull back to lower angle terrain.
  • Uncertainty is best managed through conservative terrain choices at this time.

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.