Avalanche Forecast

Issued: Feb 12th, 2019 4:21PM

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

dsaly, Avalanche Canada

Kootenay Boundary.

New storm slabs have formed over on old wind slabs and a variable wind-affected surface. As slabs gain cohesion, the chance of human triggered avalanches is likely.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

TUESDAY NIGHT: Flurries, 5-15 cm snow. Alpine temperatures near -8C. Ridgetop winds light to moderate from the southwest.WEDNESDAY: Mix of sun and cloud. Alpine temperatures near -7C. Ridgetop winds light from the northeast.THURSDAY: Cloudy with scattered flurries, trace to 10 cm snow. Alpine temperatures near -8C. Ridgetop winds light from the southeast.FRIDAY: Cloudy with isolated flurries, 10-20 cm snow. Alpine temperatures near -8C. Ridgetop winds light gusting moderate from the southwest.

Avalanche Summary

Several large (size 1-2.5) natural wind slab avalanches occurred on all aspects at treeline and above sometime late Friday evening into Saturday. Widespread wind effect was noted through the weekend with scouring and wind-loading on a variety of aspects. Small (size 1-1.5) wind slabs with 30-50 cm crown depths were reactive to skier traffic. Continued reports of whumpfing and cracking at treeline and below suggest the buried SH/crust layer down 40-60cm is still reactive. The destructive potential of avalanches failing on this layer will increase as new snow accumulates and gains cohesion.

Snowpack Summary

Around 25-40 cm storm snow fell on a collection of wind-affected surfaces found at all elevations, in alpine and upper treeline, scoured and wind-pressed surfaces in exposed areas with hard wind slabs in lee features to softer wind slabs and loose, dry snow in sheltered terrain and lower elevations. This recently covered wind-affected snow overlies a variety of snow surfaces: sun crust on southerly aspects to mountain top, variable wind-affect and wind-press in north to westerly terrain, and weak feathery surface hoar crystals down 40-60 cm 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 40-60 cm) seems to be more predominant and reactive to human triggers than the one buried deeper down (60-100 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. Below that, the snowpack is well settled.

Problems

Storm Slabs

Storm slabs have formed with new snow. Be extra cautious where new snow covers recently reactive wind slabs at upper elevations or in sheltered areas at treeline and below where it adds load over a buried layer of surface hoar.

The recent snow is now hiding windslabs that were easily visible before the snow fell.Be careful with wind loaded pockets, especially near ridge crests and roll-overs.Avoid freshly wind loaded features.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2.5

Persistent Slabs

There is a layer a layer of weak feathery surface hoar 40-60 cm below the surface and another 60-80 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.If triggered the storm and wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Possible

Expected Size

1.5 - 2.5

Valid until: Feb 13th, 2019 2:00PM