Avalanche Forecast

Issued: Mar 3rd, 2013 9:32AM

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

swerner, Avalanche Canada

Kootenay Boundary.

Avalanche danger will likely increase when the sun comes out. Be aware of your overhead hazards.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain

Weather Forecast

The pattern turns cooler, with some sunny skies under the ridge for the next two days. The next low pressure system will begin to effect the region on Tuesday, bringing cloud cover and new snow.Monday: The ridge will move over all regions and dominate the weather pattern. Lingering cloud until mid-day with sunny skies in the afternoon. Ridgetop winds light from the South. Alpine temperatures near -4 and freezing levels around 1300 m in the afternoon. Tuesday: The low will bring a milder southerly flow over the region and push a weak and poorly timed upper wave across the Kootenay, Columbias and South Rockies. Alpine temperatures -3 and freezing levels 1100 m. Ridgetop winds light from the SW. Wednesday: Moderate snow amounts with ridgetop winds light from the East. Alpine temperatures near -5 and freezing levels 1500 m falling to valley bottom overnight.

Avalanche Summary

Numerous natural slab avalanches were reported on Saturday. These occurred mainly on N-E aspects, above 2200 m and ranging from size 1.5-2.5, failing within the recent storm snow, and suspect of failing on older surface hoar layers buried down 50-60 cm. Explosive control initiated numerous size 1.5-2.5 slab avalanches on SE-SW aspects above 1600m. No new observations reported on Sunday.

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.The lower snowpack is generally well settled, and average treeline snow depths sit near 250 cm.

Problems

Storm Slabs

Recent snow and wind has formed touchy storm slabs on all aspects and elevations. If the sun comes out today, natural avalanche activity will likely increase. Rider triggering is very likely, especially on lee slopes that have been wind loaded.

Avoid cross loaded slopes at or above treeline.>Avoid areas with overhead hazard.>Be alert to conditions that change with elevation and aspect.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 5

Persistent Slabs

The presence of weak layers buried in the upper snowpack means there is a risk of triggering surprisingly 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.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 6

Cornices

Large looming cornices exist on ridgelines. These cornices may become weak and fail, especially if the sun comes out. The weight of cornice fall could trigger a slab avalanche on the slope below.

Give cornices a wide berth when travelling on or below ridges.>

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Valid until: Mar 4th, 2013 2:00PM