Avalanche Forecast

Issued: Feb 2nd, 2013 9:23AM

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

swerner, Avalanche Canada

Northwest Coastal.

The "Danger Ratings" are based on 20 cm or more snow for Sunday accompanied by strong winds. If you receive less snow, consider the rating to be one step to high.

Summary

Confidence

Fair - Forecast snowfall amounts are uncertain on Sunday

Weather Forecast

Sunday: A Pacific frontal system moves in bringing moderate to heavy precipitation amounts (25-40 mm). Ridgetop winds blowing strong from the SW. Alpine temperatures near -4.0 and freezing levels falling to 700 m. Monday: A trailing warm front moves onto the region bringing continued moisture and wind. Ridgetop winds will be strong from the South. Alpine temperatures -5.0 and freezing levels falling to 500 m. Tuesday: Unsettled conditions prevail with cloudy skies and no significant precipitation. Areas in the north may see some sunny periods. Ridgetop winds will be light from the South. Alpine temperatures near -7 and freezing levels will fall to 200 m.

Avalanche Summary

On Friday, several natural loose, slab and glide avalanches were spotted from a heli flight up to size 2.5. I suspect loose wet avalanches continued in below treeline elevations.

Snowpack Summary

New storm snow will blanket wind slabs (NE-W) that built over the past week. With strong winds from the SW, fresh wind slabs will form on lee slopes and behind terrain features like ribs and ridgelines. Lingering beneath (down 50-80 cm) sits a persistent weakness comprising of surface hoar, facets, and /or a crust. Recent test done on these layers are producing hard results with sudden and resistant planar characteristics. The mid pack is generally well settled and strong, although basal facets remain a concern in the northern part of the region.

Problems

Wind Slabs

Strong SW winds will build fresh wind slabs on lee slopes and behind terrain breaks such as ridgelines and ribs. These may be reactive under the weight of a person and/or a machine. Hollow sounds, and cracking from beneath may indicate unstable snow.

Stay off recent wind loaded areas until the slope has had a chance to stabilize.>Be alert to conditions that change with elevation.>Use ridges or ribs to avoid pockets of wind loaded snow.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 5

Persistent Slabs

Up to 80 cm sits above a persistent weakness comprising of a crust/facet/surface hoar interface. This interface may be found most reactive in sheltered areas over convex rolls or steep terrain. Dig down and see how reactive it is in your riding area.

Whumpfing is direct evidence of a buried instability.>Dig down to find and test weak layers before dropping into your line.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 6

Valid until: Feb 3rd, 2013 2:00PM