Avalanche Forecast

Issued: Jan 7th, 2013 9:46AM

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

mpeter, Avalanche Canada

Purcells.

There is significant variability in new snow amounts from west to east in the region and Wednesday's storm will vary wildly north to south. This means that local awareness and diligent travel practices are critical for the forecast period.

Summary

Confidence

Fair - Forecast snowfall amounts are uncertain on Wednesday

Weather Forecast

Tuesday: Cloudy, with precipitation building late in the day as a surface low approaches. Winds should be westerly and freezing levels may climb to 1000m.Wednesday: The surface low should bring moderate to locally heavy snowfalls with higher amounts in the southern part of the region. Freezing levels may reach 1500m as the low advances with southwest winds reaching 60km/h.Thursday: The low should pass leaving occasional flurries and eventually sunny breaks. Winds turn northeasterly and diminish to 20km/h.

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 50cm 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. In some areas the new snow is bonding poorly to these interfaces, and lots of sluffing is being reported. Where the storm snow is deeper (around 30cm), the sluffing is extensive enough to require a management plan. The deepest deposits of storm snow (pushing 50cm) are settling into a more cohesive storm slab. 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

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.>Make observations and assess conditions continually as you travel.>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 8th, 2013 2:00PM