Avalanche Forecast

Issued: Dec 1st, 2012 9:19AM

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

triley, Avalanche Canada

Purcells.

The new storm slab may be easily triggered on wind loaded pockets in the alpine.

Summary

Confidence

Fair - Due to limited field observations on Sunday

Weather Forecast

Overnight and Sunday: Light precipitation is expected to continue, bringing 3-5 mm by morning and another 3-5 during the day. The freezing level should drop down to the valley by morning and then rise to about 1100 metres during the day. The winds should remain moderate from the SW.Monday: The moisture should continue to drift in to the region from the West, 4-6 mm is forecast to fall as snow above 1000 metres. Moderate SW winds with strong gusts and alpine temperatures around -7.0Tuesday: Moderate to Heavy precipitation combined with freezing levels rising up to 1400 metres, and moderate to strong Southerly winds.

Avalanche Summary

Some avalanches up to size 2.0 have been reported from explosive control, releasing the recent storm slab down about 40 cms on NE aspects.

Snowpack Summary

The new storm slab is about 30-40 cms deep in the alpine, and is moist and well consolidated at treeline. The storm slab is sitting on a surface hoar layer that developed last week during the clear weather. Another surface hoar layer that developed during mid-november was reported to be active last week. There is a rain crust near the ground that we're calling the early November crust. There are some facets below it, or it may appear as a sandwich of crusts and facets, but it's been reportedÂ as unreactive at this time. There is still a sharp transition in snow depth from treeline to below treeline making back-country travel challenging under 1300 m in elevation.

Problems

Storm Slabs

Storm slabs continue to grow in the alpine and at treeline from the warm wet weather. Snowfall amounts may be quite variable across the region. Watch for conditions that may be quite different at higher elevations due to recent high freezing levels.

The new snow will require several days to settle and stabilize.>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

Persistent Slabs

Two problem layers exist: A surface hoar layer 30 - 60 cm below the snow surface and the early Nov. crust near the ground. It may be possible for a rider to trigger these weak layers, especially in areas where the snowpack is thin and/or rocky.

Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 5

Valid until: Dec 2nd, 2012 2:00PM