Avalanche Forecast

Issued: Jan 17th, 2018 4:37PM

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

jmcbride, Avalanche Canada

Kootenay Boundary.

Significant snowfall, strong winds and mild temperatures will add new load to an already complex and reactive snowpack. Avoid all avalanche terrain until the new snow has had a chance to settle and stabilize.

Summary

Confidence

Moderate - Freezing levels are uncertain

Weather Forecast

TONIGHT: Wet snow and rain. Precipitation 10-20 mm. Ridge wind strong, southwest. Temperature 2. Freezing level rising to 2000 m.THURSDAY: Cloudy, flurries. Accumulation 5-10 cm. Ridge wind strong, southwest. Temperature 2. Freezing level lowering to 1500 m.FRIDAY: Mostly cloudy, flurries. Accumulation trace. Ridge wind light, southwest. Temperature -2. Freezing level 1200 m.SATURDAY: Cloudy, flurries. Accumulation trace. Ridge wind light, southwest. Temperature -2. Freezing level 1100 m.

Avalanche Summary

On Monday there were reports of two skier accidentals triggered on a northwest aspect between 1980-2000 m. The first was a size 1.5 and the second, triggered about thirty minutes later, was a size 2. A natural size 2 loose wet avalanche was also report on a southwest aspect at 2100m, as well as numerous explosive triggered size 2-3.5 slab avalanches running on weak layers deep in the snowpack.Sunday there were reports of natural loose wet avalanches to size 2.5 on solar aspects as well a size 3 deep-persistent, slab avalanche on a northerly aspect that's suspected to have failed on the December 15th 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.About 5 cm of new snow now covers the January 16th surface hoar/ crust layer that formed during the most recent period of warm weather and clear nights. This crust can be found on solar aspects while surface hoar has been buried on shaded aspects above 1600m. Below the January 16th crust lies the January 5th interface which also consists of a crust/surface combination and is buried 45-70 cm below the surface. The late-December surface hoar layer is buried 75-100 cm below the surface, and the spooky mid-December surface hoar layer is now 80-130 cm below the surface. This spooky interface continues to produce sudden snowpack 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. 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

New snow and wind will build storm slabs that overlie the most recent crust/surface layer and will likely be touchy. If triggered these slabs have the potential to step down to one or more deeper weak layers buried in the snowpack.

If triggered the storm slabs may step down to deeper layers resulting in large avalanches.Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very 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 120cm below the surface. Expert level knowledge and experience is required to safely venture into the backcountry.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

2 - 3.5

Valid until: Jan 18th, 2018 2:00PM