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Avalanche Forecast

Archived

Jan 9th, 2020–Jan 10th, 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 possible, human triggered probable.
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.

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

THURSDAY NIGHT: Cloudy with clear periods, light to moderate northwest wind, alpine temperature -16 C, freezing level below valley bottom.

FRIDAY: Cloudy with snowfall, accumulation up to 10 cm, moderate southwest wind, alpine temperature -12 C, freezing level below valley bottom.

SATURDAY: Cloudy with flurries, accumulation up to 15 cm, light to moderate southwest wind, alpine temperature -8 C, freezing level at 400 m.

SUNDAY: Cloudy with snowfall, snow accumulation 5 to 10 cm, moderate to strong southwest wind, alpine temperature -8 C, freezing level below valley bottom.

Avalanche Summary

On Wednesday, a few natural and one skier triggered slab avalanche of size 3 were reported. 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. 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 10 cm snow accumulation are expected during the day on Friday. The previous 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

  • Conditions may have improved, but be mindful that deep instabilities are still present.
  • If triggered, storm slabs in-motion may step down to deeper layers and result in very large avalanches.
  • 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.