Avalanche Forecast

Issued: Jan 27th, 2018 4:35PM

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.

jsmith, Avalanche Canada

Kootenay Boundary.

New snow amounts within this region may be highly variable on Sunday. Consider the hazard to be HIGH in areas that receive more than 25 cm of new snow.

Summary

Confidence

Low - Timing, track, or intensity of incoming weather system is uncertain on Monday

Weather Forecast

SUNDAY: 5-15 cm of new snow / Moderate southwesterly ridgetop winds / Freezing level rising to around 1000m.MONDAY: 10-15 cm of new snow / Strong southwesterly ridgetop winds / Freezing level rising to around 1800m.MONDAY NIGHT: 10-20 cm of new snow / Strong to extreme southwesterly ridgetop winds / Freezing level around 1500m.TUESDAY: Cloudy with flurries / moderate southwesterly ridgetop winds / Freezing level dropping to around 1000m.

Avalanche Summary

Explosive control near Nelson triggered numerous storm slab avalanches up to size 2 on Friday. On Wednesday, over a dozen natural size 2 storm slab avalanches were reported on all aspects and elevations, though most occurred at treeline and above. Additionally, several natural persistent slabs to size 2.5 were reported on northwest to easterly aspects above 1900m. These storm slabs and the persistent slabs beneath them are expected to remain reactive to human triggers.

Snowpack Summary

The snowpack in this region is currently being described as "Complex" and "Spooky".15 cm of new snow brings recent storm snow total to approximately 75-100 cm which has been redistributed by moderate southerly winds.Currently, the primary layer of concern was buried in mid-January and is down around 60-90cm. It is composed of a mixture of surface hoar (weak, feathery crystals) and/or a crust. Numerous recent natural avalanches to size 2.5 have been reported on this sensitive layer and human triggering large, destructive avalanches on this layer remains likely.Below this layer lies a second crust/surface hoar interface buried early-January that is now 100-120 cm below the surface. The mid-December surface hoar layer is buried 120-150 cm below the surface. This 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

New snow and wind continue to create touchy storm slabs reactive to human triggers. If triggered, these slabs have the potential to step down to deeper weak layers buried in the snowpack.

If triggered the storm slabs may step down to deeper layers resulting in large avalanches.Use small slopes with low or no consequence to test the bond of the new snow.Be cautious when transitioning into wind effected terrain.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

The snowpack is complex and has produced very large avalanches on up to four separate weak layers buried 60 to 140cm below the surface. A conservative approach and moderate-angled, simple terrain are good ways to manage a complex snowpack.

Be aware of the potential for large avalanches due to the presence of buried surface hoar.Be mindful that deep instabilities are still present and have produced recent large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 3.5

Valid until: Jan 28th, 2018 2:00PM