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Avalanche Forecast

Archived

Jan 11th, 2020–Jan 12th, 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.

10 to 20 cm snow overnight and more during the day might form reactive slabs in lee terrain features where the snow is exposed to wind from the southwest. The avalanche danger will increase throughout the day with increasing snow amounts and wind.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

SATURDAY NIGHT: Cloudy with snowfall, accumulation 10 to 20 cm with highest amounts at Kootenay Pass, light westerly wind, alpine temperature -10 C, freezing level at 500 m.

SUNDAY: Cloudy with snowfall, accumulation 10 to 20 cm, light to moderate southwest wind, alpine temperature -10 C, freezing level at 500 m.

MONDAY: Mostly cloudy with snowfall, accumulation 5 to 15 cm, light westerly wind, alpine temperature -15 C, freezing level below valley bottom.

TUESDAY: Mostly cloudy with flurries, accumulation 5 to 10 cm, light to moderate westerly wind, alpine temperature -15 C, freezing level below valley bottom.

Avalanche Summary

On Saturday, a skier triggered storm slab avalanche of size 2 fully buried a person. The person was rescued by companions and sustained no injuries. A few small (size 1) natural and skier triggered storm slab avalanches were reported. Numerous large (size 2) storm slab avalanches were triggered by explosives.

On Friday, several skier triggered slab avalanches were reported up to size 2. Some of these avalanches were triggered remotely. Several small (up to size 1.5) natural avalanches were observed.

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

Snowpack Summary

The storm of the last days brought 20 to 40 cm of snow which fell with moderate 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 70 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

  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Be mindful that deep instabilities are still present and have produced recent large avalanches.

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.