Avalanche Forecast

Issued: Jan 20th, 2018 4:41PM

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.

jmcbride, Avalanche Canada

Kootenay Boundary.

Recent loading from new snow and wind has added to an already complex and tricky snowpack with several buried weak layers. Best to stick to moderate terrain and avoid wind-loaded areas.

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain

Weather Forecast

TONIGHT: Flurries. Accumulation trace. Ridge wind light, southwest. Temperature -6. Freezing level 500 m.SUNDAY: Flurries. Accumulation 5-15 cm. Ridge wind strong, south. Temperature -3. Freezing level 1200 m.MONDAY: Flurries. Accumulation 5-10 cm. Ridge wind moderate, southwest. Temperature -4. Freezing level 1200 m.TUESDAY: Mostly cloudy, flurries. Accumulation trace. Ridge wind light, south. Temperature -5. Freezing level 800 m.

Avalanche Summary

Friday there were reports of a few natural, size 1-1.5 storm slab avalanches in steep terrain. Also, two size 1, skier accidentals were triggered in steep terrain within the recent storm snow.On Thursday ski cuts and explosive control work produced numerous size 1.5-2 storm slab avalanches as well as a size 2.5 and a size 3 that stepped down to the mid-December layer on north to northwest aspects above 2000 m. .Wednesday there were reports of a skier accidentally triggering a size 1 wind slab on an east aspect at 2000 m that is suspected to have failed on the most recent mid-January surface hoar layer. And a very large whumpf was observed on a northeast aspect at 1800 m that is believed to have been associated with the mid-December layer.

Snowpack Summary

The snowpack is complex with several buried weak layers of concern that remain active and have produced several recent, large and destructive avalanches.Approximately 20-40 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 and continues to produce sudden snowpack test results. This spooky layer 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. In shallow, rocky terrain the mid-December surface hoar and the late November crust seem to be reacting together which is a volatile combination.

Problems

Storm Slabs

Recent wind and storm snow has formed cohesive slabs, particularly on lee slopes at treeline and above. If triggered these slabs have shown 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

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 130cm 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

Likely

Expected Size

2 - 3.5

Valid until: Jan 21st, 2018 2:00PM