Avalanche Forecast

Issued: Mar 6th, 2012 8:47AM

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

ccampbell, Avalanche Canada

South Coast.

Intense solar radiation may cause a spike in avalanche activity on sun-exposed slopes.

Summary

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain on Friday

Weather Forecast

Wednesday: Mostly clear with light winds and freezing levels rising to around 1200m. Thursday: Increasing high clouds throughout the day with light winds and freezing levels as high as 2500m for the southernmost part of the region. Friday: Mostly cloudy with snow increasing in the afternoon. Freezing levels around 1000m and moderate southwesterly winds.

Avalanche Summary

In the northern part of the region, recent slab avalanches reached Size 2.5 on southern aspects and Size 1.5 on all other aspects. They were mostly natural soft wind slabs on northerly aspects, but some were human triggered and suspected to have involved deeper persistent weaknesses from mid-February. In the Coquihalla Pass area recent heavy loading from snow and wind resulted in several Size 3-4 natural avalanches. Two Size 4 slab avalanches were observed on northwest through east aspects. One was a 5-10m thick slab and took out large swaths of mature forest in the runout, while the other was a relatively thin slab at 1-2m but propagated approximately 1.5 Km across a bowl.

Snowpack Summary

In the northern part of the region south aspects are described as spooky with a very hollow feeling, but all other aspects seem to be well settled with only surface instabilities. Up to 45cm of recent storm snow is sitting on a poorly bonded crust on sun-exposed slopes with easy sudden collapses below the crust, and the mid-February buried surface hoar and/or facet persistent weakness remains a concern and is particularly touchy where there is an associated crust at treeline and below and on south aspects. Meanwhile in the Cascades, 70-100cm of recent storm snow combined with five straight days of sustained extreme winds has created a highly unstable wind and storm slab problem that will probably take a few days to settle and strengthen.

Problems

Wind Slabs

Generally lurking below ridgecrests, behind terrain breaks, and in gullies. Wind slabs remain touchy and there is still a lot of snow available for reverse-loading if outflow winds pick up.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 5

Storm Slabs

Touchy weaknesses within and under the recent storm snow are expected to become more reactive with sun-exposure. Cohesionless low-density snow overlying a crust can produce large loose-snow avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 6

Persistent Slabs

Primarily in the northern region and especially touchy where there is an associated crust.The potential for remote triggering, step down avalanches, and wide propagations, makes this persistent slab problem particularly tricky to manage.

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

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

3 - 6

Valid until: Mar 7th, 2012 8:00AM