Avalanche Forecast

Issued: Dec 8th, 2012 4:28PM

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

garth lemke, Parks Canada

Jasper.

Alpine winds are expected to be strong NW starting Sunday increasing the danger especially with 20cm or more surface snow available for transport. Watch for slab conditions building and reverse loading patterns possibly into treeline locations.

Summary

Weather Forecast

Needle like surface hoar development is occurring from last 48 hrs weather. Sunday will be cold -10 to -20, likely strong NW alpine winds developing mid-day but remaining light at treeline elevations until Sunday evening. Snow will be light flurries the next few days and slight warming trend Monday to Tuesday.

Snowpack Summary

Light and variable winds continue to have little influence on recent 10-20cm storm snow. Snowpit at Parkers Slabs was 190cm thick, a well settled midpack, and no basal facets. Surface snow remains available for wind transport. That wind may arrive starting Sunday during the day causing the danger rating to increase as a result on Sunday or Monday.

Avalanche Summary

Good visibility today. Three size 2-2.5 avalanches were noted 24-48 hrs old, 40 degree plus, NW aspect, cross loaded gullys. Explosive work on parkers slabs on Thursday with 22 avalauncher rounds produced one size 2 slab avalanche in a windloaded location on smooth steep rock slab. Settlement and localized winds are creating pockets of slabs. �

Confidence

Wind effect is extremely variable on Sunday

Problems

Wind Slabs

Variable localized winds are creating this slab condition on lee aspects particularly at ridge tops and specific features such as cross loading gullies. Watch for reverse loading patterns and increase in activity as winds expected to increase Sunday.

Be careful with wind loaded pockets while approaching and climbing ice routes.Avoid lee and cross-loaded terrain near ridge crests.

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

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

1 - 3

Persistent Slabs

A persistent facetted weakness can be found around a mid-pack crust.

Avoid shallow snowpack areas where triggering is more likely.Avoid unsupported slopes.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Deep Persistent Slabs

This layer seems to be developing mainly in shallow snowpack areas due to the classic Rockies temperature gradient process.

Be aware of thin areas that may propogate to deeper instabilites.Carefully evaluate and use caution around thin snowpack areas.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

1 - 3

Valid until: Dec 9th, 2012 4:00PM