Avalanche Forecast

Issued: Feb 11th, 2019 4:43PM

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

dsaly, Avalanche Canada

Kootenay Boundary.

There is uncertainty in how incoming snowfall with interact with recent wind slabs and deeper weak layers. Treat avalanche hazard as Considerable if over 25 cm new snow accumulates.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain on Tuesday

Weather Forecast

MONDAY NIGHT: Cloudy with scattered flurries, up to 5 cm accumulation. Alpine temperatures near -15C. Ridgetop winds moderate from the south-southeast.TUESDAY: Flurries, 7-15 cm accumulation with up to 20 cm accumulating near Kootenay Pass and the US border. Alpine temperatures near -8C. Ridgetop winds moderate gusting strong from the southwest.WEDNESDAY: Mix of sun and cloud. Alpine temperatures near -8C. Ridgetop winds moderate decreasing to light from the east-southeast.THURSDAY: Cloudy with scattered flurries, trace to 5 cm accumulation. Alpine temperatures near -8C. Ridgetop winds light from the southeast.

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 were reactive to skier traffic.

Snowpack Summary

A dusting of new snow fell on a collection of wind-affected surfaces found at all elevations: scoured and wind-pressed surfaces in alpine and exposed areas with hard wind slabs in lee features, to softer wind slabs and loose, dry snow at at lower elevations and in sheltered terrain. This 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 20- 40 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 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.

Problems

Wind Slabs

Recent widespread wind effect through the region developed reactive wind slabs in steeper features and wind-loaded terrain. With 7-15 cm new snow falling Tuesday, expect new slab development and older wind slabs hidden under new snow.

Be careful with wind loaded pockets, especially near ridge crests and roll-overs.Watch for signs of instability such as whumpfing, or cracking. The recent snow may now be hiding windslabs that were easily visible before the snow fell.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 2

Persistent Slabs

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.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Unlikely - Possible

Expected Size

1 - 2

Valid until: Feb 12th, 2019 2:00PM