Avalanche Forecast

Issued: Jan 22nd, 2018 4:25PM

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

jlammers, Avalanche Canada

Kootenay Boundary.

Deep instabilities are still present in our snowpack. Conservative terrain selection remains critical.

Summary

Confidence

Moderate - Freezing levels are uncertain on Wednesday

Weather Forecast

Tuesday: 4-8cm of new snow / Moderate to strong southwesterly winds / Freezing level at 8000mWednesday: 15-30cm of new snow / Moderate southerly winds / Freezing level at 1200mThursday: Light flurries/ Light southwesterly winds / Freezing level at 800m

Avalanche Summary

On Sunday a few skier and explosives-controlled storm slab avalanches to size 1.5 were observed failing on west to northeast facing slopes between 1900m and 2050m. These avalanches occurred in response to new snow and wind. No persistent avalanches were observed over the weekend. That isn't to say that weaknesses don't exist in the snowpack and that large avalanches aren't possible. It was only a few days ago when explosives control produced a size 2.5 and a size 3 slab avalanche that stepped down to the mid-December layer on north to northwest aspects above 2000 m. Over time, we'll likely transition to a low-probability/ high consequence avalanche pattern with these buried persistent weak layers. This makes terrain selection harder as some slopes may not react to the weight of a rider, while other slopes may be waiting to surprise with nasty consequences.

Snowpack Summary

Since last Friday between 15 and 30cm of new snow fell with the greatest accumulations occurring in the Kootenay Pass area. Moderate to locally strong southwest winds have redistributed the new snow into reactive storm slabs in exposed lee terrain.Approximately 30 - 50 cm of storm snow now covers the most recent crust/surface hoar layer that was buried mid-January. This crust can be found on solar aspects while surface hoar has been buried on shaded aspects above 1600m. Below this layer lies a second crust/surface hoar interface buried early-January that is now 50-90 cm below the surface. The mid-December surface hoar layer is buried 100-140 cm below the surface. This spooky layer still produces "sudden" test results and is most pronounced at treeline, but is also present below treeline . Two laminated crusts created by rain events in late November lay just below the mid-December interface, and may co-exist with facets.

Problems

Storm Slabs

Recent wind and storm snow have formed cohesive slabs, particularly on lee slopes at treeline and above. If triggered these slabs have the potential to step down to one or more deeper weak layers buried in the snowpack.

Be cautious as you transition into wind affected terrain.Be careful with wind loaded pockets, especially near ridge crests and roll-overs.If triggered the storm slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

The snowpack is complex and has produced very large and destructive avalanches on up to four separate weak layers buried 50 to 140cm below the surface. A conservative approach and moderate-angled, simple terrain are good choices.

Be mindful that deep instabilities are still present and have produced recent large avalanches.Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 3.5

Valid until: Jan 23rd, 2018 2:00PM