Avalanche Forecast

Issued: Feb 19th, 2012 9:16AM

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

jfloyer, Avalanche Canada

Purcells.

Check out the recent Forecaster Blog post discussing the "Tipping Point".

Summary

Confidence

Fair - Intensity of incoming weather is uncertain on Tuesday

Weather Forecast

Monday and Tuesday: flurries both days bringing minimal accumulation of new snow. Light to moderate NW winds increasing to strong NW on Tuesday. Freezing level around 800 m. Tuesday night into Wednesday: a slightly stronger band of moisture arrives bringing around 10 cm new snow, freezing levels rising to 1800 m and strong westerly winds.

Avalanche Summary

On Saturday, small avalanches could be triggered in the top 20 cm of snow by ski cutting. As we get incremental amounts of new snow above this interface, we inch closer to the tipping point, when more widespread and dangerous avalanches start to occur. This concept is discussed in more detail in the latest Forecaster Blog post.

Snowpack Summary

Widespread surface hoar has been buried by around 10 cm of new snow in most of the region. The exception is terrain closer to the Bugaboos, where the interface is down 20-40cm. A melt-freeze is also associated with this weak interface on southerly aspects at all elevations. North and east aspects continue to have dry snow and some surface sloughing in steep terrain. Basal facets have not been reactive, but operators continue to monitor this layer in tests. Triggering this deep persistent weak layer is unlikely, but shallow snowpack areas or shallow weak areas adjacent to deeper wind loaded slopes are suspect locations.

Problems

Wind Slabs

Fri/Sat winds were out of the S, SW, Sun.out of the NW. This combination has set up thin wind slabs behind exposed terrain features.

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 4

Deep Persistent Slabs

Although a deep persistent slab would most likely require a large trigger (such as cornice fall), they are still possible; especially in thin snowpack areas or in unsupported, rocky terrain.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely

Expected Size

3 - 7

Valid until: Feb 20th, 2012 9:00AM