Avalanche Forecast

Issued: Mar 14th, 2016 9:31AM

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

triley, Avalanche Canada

Kootenay Boundary.

Storm slabs may be easy to trigger, and persistent slabs resulting in very large avalanches continue to be a concern for human triggering.

Summary

Confidence

Moderate - Timing or intensity of solar radiation is uncertain

Weather Forecast

Moderate westerly winds overnight with 3-5 cm of new snow and freezing levels down to valley bottoms. The precipitation is expected to be convective and may result in pockets of higher snowfall. Mostly cloudy on Tuesday with a few sunny breaks. Winds becoming moderate northwest during the day and freezing levels rising up to 1500 metres. Less cloud and more sun on Wednesday with light winds and a diurnal freeze (overnight) and thaw (up to about 1500 metres) cycle developing. Mostly sunny on Thursday with light northeast winds.

Avalanche Summary

Explosives control work on Sunday resulted in storm slab avalanches up to size 2.0 on northerly aspects, and skiers controlled avalanches up to size 1.5 on northeast aspects .On Saturday numerous human triggered storm slab avalanches to size 2 were reported on northwest, north, northeast and east facing aspects between 1800 and 2200 m. One deeper persistent slab avalanche was triggered after a snow-cat intentionally pushed a cornice onto a north facing feature at 2200 m resulting in a size 3 avalanche that was 100 cm deep on average. Check out the Mountain Information Network for more details about a human triggered size 2 avalanche on a NW facing slope along the Bonnington Traverse.

Snowpack Summary

Another 5-10 cm overnight has added to the recent storm slabs. There is now 20 to 40 cm of storm snow combined with moderate southwest winds which have likely created deep wind slabs on the leeward side of ridgecrests and mid-slope terrain features. In some drainages these storm slabs may be sitting on a thin crust that was initially buried on March 11th. A second curst, (the early March melt/freeze crust) can be found down 40 to 70 cm. A persistent weak layer buried late-February is typically down 60 to 100 cm and remains sensitive to triggering as indicated by recent avalanche activity. This weakness is widespread buried surface hoar on sheltered slopes above 1700 m, and a crust potentially with associated facets on previously sun-exposed slopes (primarily south aspects).

Problems

Storm Slabs

New snow has added to the recent storm slabs. Storm slabs may be easy to trigger where they are sitting on a crust. Storm slabs in motion may step down and release deeper persistent weak layers resulting in very large avalanches.

Avoid freshly wind loaded features.>Choose well supported conservative lines and watch for clues that indicate instability.>The new snow will require several days to settle and stabilize.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 4

Persistent Slabs

Recent storm snow has added to the load above the buried surface hoar layer from February 27th. This deeply buried weak layer continues to be a concern for triggering very large avalanches.

Surface avalanches in motion could step down and initiate persistent slab avalanches which have the potential to be large and destructive.>Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar. >

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

3 - 5

Valid until: Mar 15th, 2016 2:00PM