Avalanche Forecast

Issued: Mar 4th, 2013 8:40AM

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

swerner, Avalanche Canada

Kootenay Boundary.

Summary

Confidence

Fair - Forecast snowfall amounts are uncertain on Wednesday

Weather Forecast

Tonight and Tuesday: A weak ridge will remain over interior ranges with generally dry conditions. Ridgetop winds will blow moderate from the South. Light snow amounts. Alpine temperatures near -8 and freezing levels 900 m.Tuesday night and Wednesday: A low pressure system will move inland. Most of this system will remain South of the border, but some cloud and light precipitation will spread into the Southern Interior. Ridgetop winds will be light from the South. Alpine temperatures near -6 and freezing levels at 1400 m, falling to valley bottom overnight.Thursday: Generally clear and dry. Ridgetop winds light from the SW. Alpine temperatures near -6 and freezing levels 1400 m and then dropping 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 avalanche observations on Monday.

Snowpack Summary

In much of the region, up to 80 cm recent snow overlies older interfaces comprising of surface hoar and sun crusts. The storm slab above these interfaces has the potential for wide propagations and surprisingly large avalanches.Wind slabs and new cornice development exist at ridgelines and on lee slopes. These are likely sensitive to human triggers. Cornices may become weak under the influence of the sun, and could trigger slabs on slopes below.A strong melt-freeze crust exists at 1700 m and below and is generally bridging any deeper instabilities. The average treeline snow depths sit near 250 cm.

Problems

Wind Slabs

Recent snow and wind has formed touchy wind 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 freshly wind loaded features.>Avoid lee and cross-loaded terrain near ridge crests.>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.

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

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 5th, 2013 2:00PM