Avalanche Forecast

Issued: Jan 10th, 2014 9:15AM

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

slemieux, Avalanche Canada

Kootenay Boundary.

Summary

Confidence

Fair - Intensity of incoming weather systems is uncertain

Weather Forecast

Tonight and Saturday: A strong low pressure system will track over the province tonight leaving heavy precipitation on the region tonight and tomorrow. Around 30 mm in water equivalent is forecasted. This will be accompanied by strong winds from the S during the night and switching from the W during the day. Freezing levels are expected to rise to 1500 m tonight and lower to 1100 m tomorrow. Sunday: Another system is tracking through the province but is not expected to leave significant amounts of precipitation over the region. Moderate W winds should increase in speed during the day. Freezing levels are forecasted to rise back up to 1500 m. Monday: Light to moderate precipitation as a cold front moves across the interior with similar freezing levels.

Avalanche Summary

Several natural dry loose avalanches up to size 1.5 were reported on steep SE aspect. Also, numerous avalanches up to size 1.5 were skier triggered yesterday in the storm snow on E and S aspects. Another similar size avalanche on a N facing slope was skier triggered but is suspected to have run on a surface hoar layer buried down 50 cm.

Snowpack Summary

The significant amounts of snow forecasted tonight and tomorrow, the strong SW winds redistributing this snow and warmer temperatures is increasing the avalanche danger for tomorrow. Windslabs lee of SW winds below ridgetop in the alpine and at treeline will be very touchy and the storm snow in sheltered areas will also need time to settle. Sluffing is expected in steep terrain at all elevation and storm snow could easily run on the newly buried surface hoar in sheltered areas at treeline and below treeline. This surface hoar layer is sitting on a sun crust on S facing aspects in some locations and could be buried around 40 cm deep by tomorrow. The persistent weak layers (PWL) are a concern to avalanche professionals as they have been producing sudden planar results and show good propagation potential when tested. The end of November facet/crust or surface hoar layer down 90 cm (or 50 cm where snowpack is very thin) and the depth hoar or basal facetting are the most worrisome layers. Presently, they do not seem reactive to skier triggering but this situation may change with additional loading, rising temperatures, and strong wind.

Problems

Storm Slabs

New snow and wind loading will create instabilities in the snowpack: Windslabs in the alpine and treeline lee of SW winds, sluffing in steeper terrain and possibly storm slab at all elevation and on all aspects.

The recent snow may now be hiding windslabs that were easily visible before the snow fell.>Be cautious as you transition into wind affected terrain.>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 - 4

Persistent Slabs

It is expected that the deeper weaknesses could meet their tipping point during this storm and create large avalanches.

Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar, facet/crust and depth hoar.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 5

Valid until: Jan 11th, 2014 2:00PM