Avalanche Forecast

Issued: Feb 8th, 2013 9:02AM

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.

swerner, Avalanche Canada

Purcells.

Blue skies and fresh snow may tempt you into steeper and bigger terrain. Maintain a diligent approach to terrain selection to best manage the current conditions.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain for the entire period

Weather Forecast

A strong ridge of high pressure builds off the coast allowing a cool, dry NorthWest flow over the region with high diurnal variations. Scattered too few clouds will exist allowing some sunny alpine skies on Saturday with more predominant sunny skies on Sunday. Ridgetop winds will blow light-moderate from the NorthWest. Treeline temperatures will hover near -4 and freezing levels rising to 1100 m in the afternoon.

Avalanche Summary

Several small slab avalanches occurred size 1 from steep, cross-loaded terrain features. A skier triggered size 1.5 slab avalanche occurred from a NE aspect at 2300 m. Natural loose dry sluffing continued from steep unsupported terrain.

Snowpack Summary

Wind slabs

exist in the alpine and at treeline on lee slopes and behind ridgelines. The recent storm slab continues to settle over old interfaces comprising of surface hoar, crusts and facets down 30-50 cm. However, areas that have buried surface hoar seem to be most touchy. Continued freezing temperatures overnight have helped to strengthen the moist surface layers that developed during warm period last weekend. Watch the duration and intensity of the sun in your local riding area; it may weaken the upper snowpack. Cornices have grown and may threaten slopes below. The mid-pack is generally well settled and the average snowpack depth at treeline elevations is near 130 cm.

Problems

Wind Slabs

New wind slabs continue to be reactive to light additional loads like skiers and sledders. Areas of concern are in the immediate lees of slopes and behind terrain features like ridgelines and ribs. Cornices have grown and may threaten slopes below.

Use ridges or ribs to avoid pockets of wind loaded snow.>Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.>Highmark or enter your line well below ridge crests to avoid wind loaded pillows.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - 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.>Dig down to find and test weak layers before committing to a line.>Good group management is essential to manage current conditions safely.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 5

Valid until: Feb 9th, 2013 2:00PM