Avalanche Forecast Kootenay Boundary

Friday 8th February 2019

Avalanche Danger Ratings Fri 8th Feb 4:03PM Danger Ratings Alpine: Moderate Danger Ratings Treeline: Moderate Danger Ratings Below Treeline: Moderate Persistent Slabs Persistent Slabs Wind Slabs Wind Slabs

Avalanche Canada Forecaster: dsaly

Date Issued:

Valid Until:

The persistent slab problem may be less reactive around the Rossland Range and Big White where less snow and an unconsolidated slab exists above the weak layer.

Confidence

High -

Weather Forecast

FRIDAY NIGHT: Mostly cloudy. Alpine temperatures near -20C. Ridgetop winds moderate from the east.SATURDAY: Cloudy with sunny breaks. Alpine temperatures near -20C. Ridgetop winds moderate from the east-northeast. SUNDAY: Mix of sun and cloud, chance of flurries. Alpine temperatures near -15C. Ridgetop winds light from the southeast.MONDAY: Mix of sun and cloud. Alpine temperatures near -14C. Ridgetop winds light from the east-southeast.

Avalanche Summary

On Wednesday, a skier remotely triggered a size 1.5 slab avalanche approximately 200 m away from them off the same ridgeline that they were traveling on, the suspect failure plain being the February 1st surface hoar interface that was buried last weekend. Additionally, slab avalanches failing on this layer were also easily triggered up to size 1.5 on north and and east-southeast aspects around 2000 m early in the week. With the cold temperatures and a bit of new snow, loose dry sluffing from steeper terrain features can be expected.

Snowpack Summary

10-30 cm of snow that fell late last week now sits on variety of snow surfaces, including buried wind crust on westerly aspects, sun crust on southerly aspects to mountain top and weak feathery surface hoar crystals in sheltered areas at treeline and below. The snowpack now hosts two buried surface hoar layers. The one that was buried on February 1st (down 20-40 cm) seems to be more predominant and reactive to human triggers than the one buried deeper down (40-80 cm). This deeper layer of surface hoar may be most reactive below treeline on shady aspects but doesn't seem to be a widespread problem in the region. The mid-pack is generally well-settled and strong.

Persistent Slabs Persistent Slabs

Likelihood

Possible

Expected Size

1.5 - 2

There is a layer of weak feathery surface hoar 20-40 cm below the surface and another 40-80 cm down. The former most reactive, especially where it is sitting on a crust.

Caution around sheltered open areas at treeline and below including cutblocks, gulleys, and glades.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

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Wind Slabs Wind Slabs

Likelihood

Possible - Unlikely

Expected Size

1 - 2

Winds continue to transport loose snow and build wind slabs. Shifting winds have formed slabs on all aspects, the most reactive will be in wind-loaded and cross-loaded terrain.

Watch for signs of instability such as whumpfing, hollow sounds, or shooting cracks.Be careful with wind loaded pockets, especially near ridge crests and roll-overs.

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

Elevations: Alpine, Treeline.

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