Avalanche Forecast

Issued: Feb 12th, 2013 8:06AM

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

pmarshall, Avalanche Canada

Purcells.

Summary

Confidence

Fair

Weather Forecast

Wednesday: Light snow early then a mix of sun and cloud. The freezing level is around 1200 m. Winds are light to moderate from the northwest. Thursday: A mix of sun and cloud. The freezing level is near valley bottom. Winds are light from the northwest. Friday: A mix of sun and cloud. The freezing level could jump as high as 1400 m. Winds are light to moderate from the southwest.

Avalanche Summary

There was one new report of a accidentally triggered size 2 slab avalanche from the Dogtooth Range. This slide was triggered on a west aspect in the alpine. It released on a layer of faceted snow overlying a melt-freeze crust (Jan 23 interface) approximately 40-50 cm deep. There were also few natural cornice triggered slab avalanches up to size 2.

Snowpack Summary

The snow surface consists of new wind slab in exposed alpine terrain, a sun crust on solar aspects, and surface hoar and/or facets on shady slopes - all getting dusted by new snow on Tuesday. The recent storm slab continues to settle over old interfaces comprising of surface hoar, crusts and facets down 30-50 cm (Jan 23 interface). One recent snowpack test from the Dogtooth Range on a west aspect in the alpine gave moderate "pops" results and showed potential for propagation on a this facet/crust layer. Continued freezing temperatures overnight have helped to strengthen the snowpack at lower elevations.The mid-pack is generally well settled and the average snowpack depth at treeline elevations is near 130. Cornices have grown and may threaten slopes below.

Problems

Wind Slabs

Wind slabs may be reactive to light loads like skiers or snowmobiles. Areas of concern are steep open slopes immediately lee of ridges and terrain features.

Be cautious as you transition into wind affected terrain.>Use ridges or ribs to avoid pockets of wind loaded snow.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 4

Persistent Slabs

The recent storm snow continues to settle into a cohesive slab above weak layers and variable old surfaces that comprise of buried wind slabs, surface hoar, and crusts. These weak layers exist 30-50 cm below the surface.

Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 5

Valid until: Feb 13th, 2013 2:00PM