Avalanche Forecast

Issued: Mar 2nd, 2013 9:24AM

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

swerner, Avalanche Canada

Kootenay Boundary.

Summary

Confidence

Fair - Intensity of incoming weather is uncertain on Sunday

Weather Forecast

The Boundary will have one more day under a complex weather scenario but the ridge will begin to take hold late tomorrow.Overnight Saturday/Sunday: Overnight will bring moderate precipitation amounts just before the cold front exits the region in the morning. The front will be trailed by a building ridge of high pressure that will bring cooler and drier conditions under a light north-westerly flow. Ridgetop winds will blow moderate from the NW. Alpine temperatures near -6 and freezing levels falling to 1000 m.Monday: Mainly dry, cooler conditions with clearing sunny skies. Ridgetop winds will be light from the South. Alpine temperatures near -4 and freezing levels around 1200 m.On Tuesday and Wednesday a deep upper low over the eastern Pacific will push more snow from southerly directions over the southern half of BC again.

Avalanche Summary

Many skier triggered slab avalanches occurred on Friday. These ranged from size 1-2, mainly on northerly aspects above 1900m and failing within the recent storm snow. Explosive control initiated numerous size 2.5 slab avalanches on SE-SW aspects above 1900m.

Snowpack Summary

In much of the region, up to 80 cm recent snow overlies weak interfaces comprising of surface hoar and sun crusts that developed mid-February. The storm slab above these interfaces has the potential for wide propagations and surprisingly large avalanches, especially where winds have shifted the snow into slabs in the lee of terrain breaks. A thin freezing rain/rime crust formed last Friday, which is now buried by about 20-40cm snow. I'm uncertain of its distribution and reactivity, but am hesitant to disregard it until with get through this stormy period.In the Rossland Range, surface hoar which was buried mid-week is 20-35 cm down and exhibits easy, sudden results in snowpack tests. As more snow builds over this layer, it could become touchy.Older snowpack weaknesses buried deeper in the pack are still being tracked by professionals. There is some potential for triggering one of these deeper layers with a large trigger. The lower snowpack is generally well settled, and average treeline snow depths sit near 250 cm.

Problems

Storm Slabs

New snow and wind will continue to build touchy storm slabs on all aspects and elevations. Natural avalanches are likely and rider triggering is very likely, especially on lee slopes that have been wind loaded.

Avoid lee and cross-loaded terrain near ridge crests.>Avoid areas with overhead hazard.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 4

Persistent Slabs

The presence of weak layers buried in the upper snowpack means there is a risk of triggering surprisingly large large slab avalanches. The weak layers may be more reactive with additional loading from new snow, and wind.

Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar and sun crusts.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 6

Valid until: Mar 3rd, 2013 2:00PM