Avalanche Forecast

Issued: Dec 27th, 2017 4:33PM

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.

jlammers, Avalanche Canada

Kootenay Boundary.

Don't be fooled by the Moderate danger ratings. Buried weak layers still exist and may surprise in isolated terrain with nasty consequences.

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain on Thursday

Weather Forecast

Wednesday night: 10-15cm of new snow / Moderate westerly winds / Alpine temperature of -13Thursday: 10-15cm of new snow / Light to moderate westerly winds / Alpine temperature of -13Friday: 5-10cm of new snow / Light and variable winds / Alpine temperature of -9Saturday: Mix of sun and cloud / Light and variable winds / Alpine temperature of -13

Avalanche Summary

On Tuesday, a skier triggered a size 1.5 wind slab on a north-facing alpine slope in Kokanee Glacier Provincial Park. The skier went for a short ride, but was uninjured in the event. No other recent avalanches have been reported. As new snow accumulates over the next few days, fresh wind slabs should remain on your radar. More importantly, the December 15th interface will become deeper. With that, the overlying slab may settle and gain cohesion increasing the likelihood of triggering of this buried persistent weak layer.

Snowpack Summary

By Thursday morning, up to 15cm of low density snow is expected to have fallen. Moderate west winds are forecast to shift these accumulations into deeper deposits in high elevation lee terrain. The new snow overlies recently buried surface hoar, although at this point not much is known about the size or distribution of this potential weak layer.Between 30 and 75cm below the surface you'll find the December 15th interface which consists of a melt-freeze crust on steep, solar, higher elevation slopes and well-developed surface hoar which seems most pronounced in sheltered treeline terrain and below. The bond at this variable interface is of critical importance, especially in areas where the overlying slab is deep and well-consolidated.The late November crust is now buried 60-100 cm and has been producing hard, resistant results in recent snowpack tests. Beneath this crust the lower snowpack is strong and well-settled.

Problems

Wind Slabs

Continued snowfall and moderate winds are forecast to create soft yet reactive wind slabs on Wednesday night and Thursday. If the snow feels hollow or stiff, wind slabs may be larger than expected.

Be careful with wind loaded pockets, especially near ridge crests and roll-overs.The recent snow may now be hiding windslabs that were easily visible before the snow fell.Be cautious as you transition into wind affected terrain.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Persistent Slabs

A well-developed layer of surface hoar is buried up to 75cm below the surface. Use extra caution in sheltered areas at and below treeline, especially if the overlying slab is thick and cohesive.

Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Dec 28th, 2017 2:00PM