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Avalanche Forecast

Archived

Jan 10th, 2020–Jan 11th, 2020

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

Regions

Kootenay Boundary.

The recent storm snow is gaining strength. However, it might still be possible to trigger deeper weak layers in the snowpack. If triggered wind or storm slab avalanches in-motion may step down to deeper weak layers and result in very large avalanches.

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength. Forecast snowfall amounts are uncertain.

Weather Forecast

FRIDAY NIGHT: Cloudy with snowfall, accumulation 5 to 10 cm, light southwest wind, alpine temperature -8 C, freezing level at 500 m.

SATURDAY: Cloudy with snowfall, accumulation 5 to 10 cm, light southwest wind, alpine temperature -6 C, freezing level rising to 800 m.

SUNDAY: Cloudy with snowfall, accumulation 5 to 10 cm, light to moderate westerly wind, alpine temperature -11 C, freezing level below valley bottom.

MONDAY: Mostly cloudy with snowfall, accumulation 5 to 10 cm, light to moderate westerly wind, alpine temperature -18 C, freezing level below valley bottom.

Avalanche Summary

On Thursday, no new avalanches were reported, but one small (size 1) explosive triggered avalanche.

On Wednesday, several natural and one skier triggered slab avalanche of size 3 were reported. Most of these avalanches released on a weak layer consisting of feathery surface hoar which was buried at the end of December and is now between 50 and 120 cm deep. One avalanche released in the storm snow and stepped down to the ground. Numerous explosive triggered storm slab avalanches of up to size 3 were reported.

On Tuesday, a widespread natural avalanche cycle occurred in the region with large storm slab avalanches to size 3.5. Numerous explosive and skier triggered storm slab avalanches up to size 2.5 were reported.

Snowpack Summary

Up to 15 cm of new snow is expected during the day adding to the new snow received on Friday. The last storm delivered around 40 to 70 cm of snow which fell with strong southwest wind. The formed slabs may still be sensitive, particularly in exposed lee terrain features. 

Deeper in the snowpack, a few layers of weak and feathery surface hoar may still be found around 50 to 150 cm deep. It is unclear whether they are still problematic and if so, how long they will be so for. The base of snowpack is also weak in parts of the region, where it consists of sugary faceted snow around a melt-freeze crust. Until these weak layers can be ruled out, best to travel conservatively.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Avalanche hazard may have improved, but be mindful that deep instabilities are still present.
  • Don't let the desire for deep powder pull you into high consequence terrain.

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.