Avalanche Forecast

Issued: Jan 6th, 2013 9:18AM

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

mpeter, Avalanche Canada

Purcells.

Conditions have changed dramatically. There is significant variability from west to east in the region. Be locally aware as to the amount of new snow and how it is bonding to the underlying surfaces.

Summary

Confidence

Fair - Forecast snowfall amounts are uncertain

Weather Forecast

Monday: Expect clouds to build with precipitation beginning in the afternoon and continuing through the evening. Up to 15cm are possible. Temperatures should reach -8 with light west winds.Tuesday: Flurries are possible with light accumulations and temperatures of -10. Winds stay westerly but increase through the day before easing overnight.Wednesday: Another wave of precipitation with accumulations of 25cm possible. Winds turn southerly with temperatures reaching -7.

Avalanche Summary

Small windslabs up to size 1.5 have been reported, failing in immediate lee locations of ridgelines. Sluffing up to size 1.5 continues.

Snowpack Summary

On the west side of the region up to 30cm of low density new snow overlies the January 4th interface while on the east side the new snow totals around 10cm. Moderate and strong south/southwest winds have redistributed this new snow into small windslabs in immediate lee features in the alpine and exposed treeline and these windslabs are reactive to human triggering.The January 4th interface consists predominantly of loose facets up to 30cm deep. In isolated locations (sheltered treeline and below treeline) surface hoar is present and there is a sun crust on steep south and west facing terrain. High in the alpine in exposed locations, old windslabs linger. The new snow is bonding poorly to these interfaces, and lots of sluffing is being reported. Where the storm snow is deeper, the sluffing is extensive enough to require a management plan.The midpack is well bonded and strong. The deep crust/facet combo from early November still exists and concern remains (although unlikely) for triggering this layer from a shallow spot.

Problems

Wind Slabs

Watch for newly formed windslabs by W and SW winds and old, buried windslabs in lee and cross loaded terrain features.

Avoid freshly wind loaded features.>Use ridges or ribs to avoid pockets of wind loaded snow.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Storm Slabs

Sluffing falls under this concern. Where there is less new snow, expect it to stay loose when triggered, but where there is more than 20cm of storm snow, expect a more cohesive slab.

On steep slopes, pull over periodically or cut into a new line to manage sluffing.>Assess start zones carefully and use safe travel techniques.>Dig down to find and test weak layers before committing to a line.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 4

Valid until: Jan 7th, 2013 2:00PM