Avalanche Forecast

Issued: Feb 13th, 2013 9:40AM

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

triley, Avalanche Canada

Purcells.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain on Friday

Weather Forecast

Overnight and Thursday: Mostly clear with cold temperatures overnight and nil precipitation. Strong Westerly winds are expected to decrease to moderate Northwesterly by morning. Freezing levels down to the valley bottom overnight, and then rising up to about 1300 metres during the day.Friday: Moderate to strong Â Northwest winds with Alpine temperatures around -5.0 and freezing levels rising to around 1600 metres. Expect broken skies and periods of strong solar radiation.Saturday: The ridge of high pressure is expected to flatten and move off to the East. An upper trough is expected to bring flurries and light snow falls to the region by the afternoon.

Avalanche Summary

There was one report of a natural size 2.0 wind slab release on a North aspect in the alpine from a shallow snowpack area.

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.>Choose well supported terrain without convexities.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 5

Valid until: Feb 14th, 2013 2:00PM