Avalanche Forecast Kootenay Boundary

Thursday 7th February 2019

Avalanche Danger Ratings Thu 7th Feb 4:41PM Danger Ratings Alpine: Moderate Danger Ratings Treeline: Moderate Danger Ratings Below Treeline: Moderate Persistent Slabs Persistent Slabs Wind Slabs Wind Slabs

Avalanche Canada Forecaster: swerner

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

THURSDAY NIGHT: 2-5 cm of new snow. Alpine temperatures near -14 and ridgetop winds light from the northeast.FRIDAY: Cloudy with snow amounts 5-10 cm. Alpine temperatures near -11 and ridgetop winds moderate from the northeast.SATURDAY: Cloudy with isolated flurries. Alpine temperatures near -16 and ridgetop winds moderate from the northeast. SUNDAY: Mix of sun and cloud with alpine temperatures near -14. Ridgetop winds mostly light from the northeast.

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, these slabs were also easily triggered up to size 1 from northerly aspects at 2000 m. 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 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 - 2

There is a layer 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 treeline and below including cutblocks, gullies and glades.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

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Wind Slabs Wind Slabs

Likelihood

Possible - Unlikely

Expected Size

1 - 2

Shifting winds have formed reactive wind slabs predominantly on southerly aspects.

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

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

Elevations: Alpine, Treeline.

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