Avalanche Forecast

Issued: Jan 7th, 2015 8:43AM

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.

triley, Avalanche Canada

South Columbia.

The storm is over and the new storm slab may take several days to settle and bond to the old surface. The mid-December buried surface hoar crust combination is expected to continue to be a tricky problem to solve.

Summary

Confidence

Fair

Weather Forecast

Warm air that has been trapped in the alpine should move out and let the alpine cool down to about -3 by Thursday morning. The freezing level should also drop down to valley bottoms overnight, and stay there throughout the forecast period. Moderate Northwest winds overnight should become light Northerly by Thursday morning. Light winds, cooling temperatures, and clearing skies are expected during the day Thursday. Mostly overcast with light Southerly winds on Friday. Flurries beginning Friday evening and becoming light snow by Saturday morning. Saturday should be overcast with flurries or light snow combined with moderate Westerly winds.

Avalanche Summary

Widespread natural avalanches reported up to size 3.0 on Tuesday. Explosives controlled avalanches up to size 3.0 on Wednesday. I suspect that natural avalanche activity ended on Wednesday and that human triggered avalanches continue to be likely-very likely. New storm slab avalanche activity is expected to become less likely, but persistent slab activity may continue for some time.

Snowpack Summary

There has been about 60 cm of new snow in the Monashees, and about 50 cm in the Selkirks in the past 48 hours. On Tuesday warm (above freezing) air moved into the alpine and freezing levels climbed up to about 1800 metres. I suspect that the warm temperatures caused rapid settlement in the dry storm slab resulting in a higher likelihood of triggering. Rain or freezing rain have created a moist slab at treeline in the Monashees. The Selkirks may be a bit cooler and drier; alpine temperatures around Revelstoke were -2.0 on Tuesday afternoon. The new storm slab is 60-80 cm thick and is sitting on a mix of old surfaces including patchy surface hoar and old windslabs on most aspects. Deeper down (around 100 cm) the mid-December surface hoar/crust layer continues to allow for remote triggering and long fracture propagations.

Problems

Storm Slabs

The new storm slab may continue to be triggered by light additional loads. Watch for areas in the alpine and at treeline where the new snow has been transported into windslabs by either Northwest or Southwest winds.

Give cornices a wide berth when travelling on or below ridges.>Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

2 - 5

Persistent Slabs

The persistent weak layer of buried surface hoar and crust continues to be a concern for remote and human triggering. This layer is now down more than a metre and may result in very large and destructive avalanches.

Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

3 - 6

Valid until: Jan 8th, 2015 2:00PM