Avalanche Forecast

Issued: Mar 5th, 2012 9:36AM

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

swerner, Avalanche Canada

South Columbia.

Summary

Confidence

Good

Weather Forecast

The region will continue to see unsettled weather conditions overnight Monday, bringing light snow (5-10 cm) with moderate Northerly winds. Freezing levels will fall to valley bottom. Tuesday: Flurries in the morning. Freezing levels remain valley bottom. Wednesday: Mix of sun and clouds. Ridgetop winds moderate from the NW. Treeline temperatures near -8. Freezing levels at valley bottom, rising 800-1000 m in the afternoon. Thursday: Dry, sunny conditions with rising freezing levels 15-2000 m. Ridgetop winds light from the SW.

Avalanche Summary

A natural avalanche cycle began on Saturday in response to snow, wind and warming. Operators are reporting numerous size 1-3.5 natural avalanches, starting in the alpine on all aspects. Skier-triggered slabs were also reported in the size 1-2 range, failing on storm snow weaknesses. Previously this week, many avalanches were triggered remotely (from several hundred metres away) and accidentally by skiers and machinery. These avalanches failed on upper snowpack persistent and storm snow weaknesses, on a variety of aspects and elevations.

Snowpack Summary

Over the weekend, 50-70 cm storm snow fell. Strong winds from the SW and fluctuating temperatures are a perfect recipe for storm slab, and wind slab instabilities. This new snow has buried variable old surfaces (surface hoar, facets, and crusts) that formed mid-February. These persistent weak layers have remained touchy all week and are a key concern at all elevations. Storm slabs, wind slabs, sluffs, and riders could trigger these deeper layers, creating avalanches which are larger than you expect. Large cornices have formed and loom as potential triggers for deep avalanches.

Problems

Storm Slabs

Storm snow with fluctuating temperatures are the perfect recipe for storm slab development. Storm slabs could step down to a persistent weak layer, creating surprisingly large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 6

Wind Slabs

Strong winds are creating widespread wind slabs, even at treeline. Large cornices have formed, they may threaten slopes below.

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

Elevations: Alpine, Treeline.

Likelihood

Very Likely

Expected Size

1 - 6

Persistent Slabs

Touchy persistent weak layers, found at all elevations, are tricky to manage. These may be triggered naturally during the storm, or by a light additional load, like a sled or skier, even on low-angled slopes or from a distance.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 7

Valid until: Mar 6th, 2012 8:00AM