Avalanche Forecast Kootenay Boundary
Saturday 9th February 2019
Strong winds have redistributed loose snow forming touchy wind slabs. The deepest and most sensitive deposits will be in wind-loaded features: around ridges and rolls, under cornices, and in cross-loaded terrain.
Moderate - Wind effect is extremely variable
SATURDAY NIGHT: Cloudy with starry breaks. Alpine temperatures near -20C. Ridgetop winds moderate from the east. SUNDAY: Mix of sun and cloud, isolated flurries in evening, trace accumulation. Alpine temperatures near -14C. Ridgetop winds light from the south.MONDAY: Mix of sun and cloud, isolated flurries in evening, trace accumulation. Alpine temperatures near -15C. Ridgetop winds light from the southeast.TUESDAY: Cloudy with scattered flurries, 5-10 cm accumulation. Alpine temperatures near -15C. Ridgetop winds moderate from the southeast.
Several large (size 1-2.5) natural wind slab avalanches occurred on all aspects at treeline and above sometime late Friday evening. Widespread wind effect was noted through Friday with scouring and wind-loading on a variety of aspects. Small wind slabs (size 1-1.5) were reactive to skier traffic. 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.
Winds are redistributing 10-30 cm of low density snow, scouring exposed aspects and developing pockets of touchy wind slabs in lee terrain. This wind-affected snow covers 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.
Likely - Possible
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Touchy wind slabs have been reported on south and east aspects. Forecasted winds are variable in both speed and direction and will continue to transport loose snow and develop slabs. The most reactive slabs will be in wind- 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, West.
Elevations: Alpine, Treeline.
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 at treeline and below including cutblocks, gulleys, and glades.
Aspects: All aspects.
Elevations: Treeline, Below Treeline.