Avalanche Forecast

Issued: Mar 5th, 2016 8:50AM

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

triley, Avalanche Canada

Kootenay Boundary.

Forecast strong winds, high freezing levels, and heavy rain or snow are expected to rapidly increase the likelihood of triggering slab avalanches.

Summary

Confidence

Moderate - Freezing levels are uncertain on Sunday

Weather Forecast

Cloud developing Saturday evening, and then strong southerly winds with 10-15 cm of new snow overnight. The freezing level is uncertain, some models (NAM and LAM) are showing close to 2500 metres overnight for specific points in the region, and the regional model is showing closer to 2000 metres. Another 15-20 cm of new snow (or rain) is expected during the day Sunday combined with strong southwest winds. Freezing levels dropping to 1000 metres by Monday morning. Mostly sunny on Monday with strong solar radiation and freezing levels around 1500 metres. Cloudy with light precipitation on Tuesday.

Avalanche Summary

Skier accidental, remotely triggered slab avalanches, and natural avalanches up to size 2.0 were reported on Friday. Explosives also released cornices up to size 3.0. On Thursday, a size 1.5 storm slab was ski cut on a northwest aspects at 2050m. This slab failed on the late-February surface hoar layer down 30-50cm. Numerous small ski cut avalanche were also reported to be failing on this layer through the region. Natural slab avalanche activity is expected during the storm on Sunday due to the combination of new snow or rain, strong winds, and warm temperatures, which is expected to overload the weak surface hoar layer from late February.

Snowpack Summary

Forecast rain and high freezing levels may rapidly increase the likelihood of triggering storm slabs and persistent weak layers. New snow and wind has added to the 30-50cm of recent storm snow that overlies a layer of well-developed surface hoar (up to size 20mm) which is very reactive to human triggers. This layer is widespread above 1700m except on south aspects where the interface was cooked by the sun and now exists as a buried sun crust. Significant wind transport has been noted so expect to find deeper, more destructive slabs in exposed lee terrain. 80-100cm below the surface you will likely find the mid-February crust/facet/surface hoar layer. Although this layer has become less likely to trigger, avalanches failing at this interface could be large and destructive.

Problems

Storm Slabs

Storm slabs are expected to continue to develop with forecast new snow or rain, and wind. Storm slabs may be sitting on a crust or crust/surface hoar combination down 30-50 cm that is easy to trigger and may result in wide fracture propagations.

Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain. >Be aware of the potential for wide propagations and remote triggers due to the presence of buried surface hoar. >

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 4

Persistent Slabs

An old weak layer down 80-100cm has been dormant recently but could wake up this weekend with substantial warming and storm loading. High freezing levels and rain may result in persistent weak layers "waking up."

Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar. >Dig down to find and test weak layers before committing to a big line. >

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

3 - 6

Valid until: Mar 6th, 2016 2:00PM