Avalanche Forecast

Issued: Feb 2nd, 2013 9:07AM

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

swerner, Avalanche Canada

Northwest Inland.

Summary

Confidence

Poor - Due to variable snowpack conditions

Weather Forecast

Sunday: A Pacific frontal system moves in bringing moderate precipitation amounts (10-15 mm). Ridgetop winds blowing strong from the SW. Alpine temperatures near -4.0 and freezing levels falling to 500 m. Monday: A trailing warm front moves onto the region bringing continued moisture and wind. Ridgetop winds will be strong from the SW.Â Alpine temperatures -6.0 and freezing levels falling to valley bottom. Tuesday: Unsettled conditions prevail with mix of sun and cloud and no significant precipitation. Ridgetop winds will be light from the South. Alpine temperatures near -7 and freezing levels will rise to 800 m.

Avalanche Summary

Natural sluffing from steep terrain features.On Thursday, a remote triggered slab avalanche size 2.0 initiated 50 m away from the skier at treeline elevation. Another report of a size 2.0 slab avalanche (skier triggered) also occurred. Both incidents were at 1200-1300 m on North aspects with crowns 50-60 cm deep, 30-40 m wide, and running up to 150 m in length.

Snowpack Summary

Touchy wind slabs have built on lee slopes (N-SW) and behind terrain features likes ribs and ridges. Up to 50 cm buried a variety of old surfaces including old wind slabs, scoured thin slopes, crusts and surface hoar. This interface has shown reactivity to rider triggers, especially around treeline and below treeline elevations. Warmer temperatures have promoted some settlement and consolidated the recent snow into slab-like characteristics. With little observations from the field it's hard to get a good handle on how widespread this layer is. I stress the importance to dig down and test weak layers. Become familiar with the snowpack in your neck of the woods.The average snowpack depth at treeline is near 100 cm but remains quite inconsistent across the region. A strong mid-pack currently overlies a weak base layer of facets/depth hoar. Triggering of this basal weakness may still be possible from thin spots, rocky outcrops or under the weight of larger triggers such as cornice fall and larger amounts of new storm snow.

Problems

Wind Slabs

New snow and strong shifting winds will build touchy wind slabs that are likely found behind terrain breaks such as ridges and ribs. Hollow sounds and cracking snow is a good indicator of unstable snow.

Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.>Use ridges or ribs to avoid pockets of wind loaded snow.>Lee and cross-loaded terrain near ridge crests is more susceptible to rider triggers.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 5

Persistent Slabs

Buried beneath the new snow sits a surface hoar/crust/facet weakness. This may be sensitive to rider triggers in steeper sheltered terrain or over convex rolls, especially at treeline and below treeline elevations.

Dig down to find and test weak layers before committing to a line.>Extra caution if traveling through open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 5

Deep Persistent Slabs

A deeply buried weak layer near the base of the snowpack could be triggered by large loads such as a cornice collapse or from a thin-spot trigger point.

Be aware of thin areas that may propagate to deeper instabilites.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 6

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