Avalanche Forecast

Issued: Feb 10th, 2013 9:01AM

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

swerner, Avalanche Canada

South Columbia.

Summary

Confidence

Fair - Timing of incoming weather is uncertain on Tuesday

Weather Forecast

Monday: The pattern and flow will start to change today as the ridge moves southward and a zonal flow sets up. An embedded cold front will move through the region bringing moderate West winds and a trace of snow. Treeline temperatures will sit near -3 and freezing levels will be around 1100 m. Tuesday: The fast paced zonal flow will continue with a trough moving in from the West bringing moderate Westerly winds and light-moderate snow accumulations. Westerly upslope areas may see more accumulations. Treeline temperatures will be near -5 and freezing levels around 1100 m.Wednesday: Another ridge is building bringing dryer conditions; especially for the short term. Ridgetop winds moderate from the SW. Treeline temperatures -9 and freezing levels near 700 m falling to valley bottom overnight.

Avalanche Summary

On Saturday, several natural slab avalanches up to size 2.5 were reported from steep slopes on a variety of aspects 1700 m and above. Suspect failing layer was the early Feb surface hoar/crust and triggered by wind. Several rider triggered avalanches were reported up to size 2 above 1900 m on most aspects and the early Feb interface being the main culprit.

Snowpack Summary

Up to 40 cm of new snow adds to the recent storm slab which sits on a surface hoar layer and a sun crust layer that developed at the beginning of February. This layer continues to be reactive to rider triggers. Deeper down (between 40-80 cm) sits an old sun crust and well preserved surface hoar that was buried on January 23rd. This persistent slab has been reactive over the past few days, especially from solar aspects. Recent snowpack tests on this layer have shown moderate compression results with sudden planar to resistant planar characteristics. Wind slabs exist in specific locations in the alpine and at treeline. The loading pattern may change due to winds switching from the SW to the NW and form pockets of wind slab in unsuspecting places.The mid-pack is well settled and strong. Cornices loom and threaten slopes below.

Problems

Wind Slabs

Wind slabs exist on lee slopes and behind terrain features like ribs and ridges. Recent changing winds may load unsuspecting aspects and catch you by surprise. Cornices may threaten slopes below.

Avoid freshly wind loaded features.>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 - 4

Persistent Slabs

Persistent slabs are 40-80 cm thick and continue to be reactive above variable sliding surfaces comprising of surface hoar, crusts and facets. They may be triggered by the weight of a skier or a machine.

Whumpfing is direct evidence of a buried instability.>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: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 5

Valid until: Feb 11th, 2013 2:00PM