Avalanche Forecast

Issued: Jan 23rd, 2017 4:54PM

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is low. Known problems include Wind Slabs and Persistent Slabs.

cgarritty, Avalanche Canada

Kootenay Boundary.

Wind slabs have combined with a persistent slab to form complex avalanche hazard in our region. Low snow areas are especially concerning.

Summary

Confidence

Moderate -

Weather Forecast

Tuesday: Mainly cloudy with possible isolated flurries bringing a trace of new snow. Winds light from the northwest. Freezing level to 800 metres with alpine temperatures of -8. Wednesday: Mainly cloudy with isolated flurries and a trace of new snow. Winds light from the northwest. Freezing level to 600 metres and alpine temperatures around -10. Thursday: Mainly cloudy with isolated flurries and a trace of new snow. Winds light from the northwest. Freezing levels around 700 metres with alpine temperatures to -9.

Avalanche Summary

Preliminary information regarding the backcountry skier fatality on Saturday is that it occurred on a S/SE facing aspect near 2050m in a cross-loaded feature. Reports from Sunday include several natural Size 1-1.5 wind slab avalanches that occurred on a northwest aspect after a bout of rapid wind loading over the morning.We also had a great MIN report of a cornice-triggered Size 2 on Friday near Cabin Peak in the Bonnington range. The initial failure was in the storm slab on a southeast aspect near 2000m but more significantly was observed stepping down to trigger a weak layer deeper in the snowpack.

Snowpack Summary

A complex and tricky snowpack exists in the Kootenay Boundary region. By Sunday morning another 3-12 cm added to the previous 35-55 cm of fresh snow from last week (which was accompanied by moderate to strong southerly winds). This resulted in touchy storm and wind slabs bonding poorly to the previous snow surface that includes facets and large surface hoar on sheltered slopes and/or a sun crust on steep sun-exposed aspects. The Jan 17th surface hoar layer continues to give easy sudden results in snowpack tests (down anywhere from 30 to 60cms depending on location). In some areas of the Rossland range, the mid-November rain crust / facet layer is now likely down 60-100 cm and has become reactive with continued loading and warming. In thin rocky areas, particularly in the Rossland range, recent reports include easy sudden collapse snowpack test results on facets down 120-150 cm near the ground. This deep persistent weakness may also become reactive with continued loading and warming.

Problems

Wind Slabs

Watch out for touchy pockets of wind slab lingering on exposed northerly features near ridge crests, and also in cross-loaded southeast gullies at treeline.

Enter your line well below ridge crests to avoid wind loaded pillows.Be cautious as you transition into wind affected terrain.Use caution in lee areas. Recent wind loading has created wind slabs.

Aspects: North, North East, East, South East, South, South West.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

Several different persistent weak layers are buried 60-150 cm deep and have proven reactive to human triggering. Conservative terrain use is essential in managing the problem, especially in low snow areas such as the southwest portion of the region.

Be aware of the potential for full depth avalanches due to deeply buried weak layers.Carefully evaluate terrain features by digging and testing on adjacent, safe slopes. If triggered the storm slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 3

Valid until: Jan 24th, 2017 2:00PM