Avalanche Forecast

Issued: Mar 1st, 2013 10:10AM

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

swerner, Avalanche Canada

Kootenay Boundary.

Summary

Confidence

Fair - Intensity of incoming weather is uncertain on Saturday

Weather Forecast

Saturday: A ridge of high pressure over the Kootenay region eases precipitation to light amounts during the day and moderate amounts developing in the evening. Strong winds easing to moderate from the SW. Â High diurnal temperature trends and freezing levels rising to 2200 m. Sunday: Light-moderate precipitation accompanied by moderate-strong ridgetop winds from the NW. Alpine temperatures near -7 and freezing levels falling to 900 m. Monday: No significant precipitation expected with ridgetop winds blowing light form the South. Alpine temperatures near -8, and freezing levels hovering around 1200 m in the afternoon.

Avalanche Summary

On Thursday natural slab avalanche activity occurred on SE aspects around 1800 m up to size 1.5. Throughout the region loose dry sluffing occurred from steeper terrain features on all aspects and elevations. I expect the avalanche activity has ramped up and will persist through the weekend with additional precipitation, rising freezing levels and strong ridgetop winds.

Snowpack Summary

In much of the region, up to 80 cm recent snow overlies weak interfaces buried in mid-February (mainly surface hoar/ sun crust layers). 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.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 in the upper snowpack (Feb 4th and Jan 23 surface hoar/facet/sun crust layers) are still being tracked by professionals. There is some potential for triggering one of these deeper layers with a large trigger like an avalanche in motion, or from a thin-spot trigger point. The lower snowpack is generally well settled.

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 all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>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, wind and rising freezIng levels.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 6

Loose Wet

Rising freezing levels in combination with new snow and rain may produce loose wet avalanches from steeper terrain features within the upper snowpack.

Surface snow may become weak with rising freezing levels, watch for wet loose avalanche activity, especially where terrain traps exist below.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 3

Valid until: Mar 2nd, 2013 2:00PM