Avalanche Forecast

Issued: Apr 10th, 2017 4:00PM

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

conrad janzen, Parks Canada

Banff Yoho Kootenay.

Excellent spring skiing continues with new snow in the forecast for Tuesday. Keep in mind that it is still possible to trigger the deep persistent facets in steep terrain, especially from thin areas or with large triggers such as cornices.

Summary

Weather Forecast

Unsettled spring weather could bring as much as 10-15cm of new snow on Tuesday with light SE winds and temperatures remaining cool. Freezing levels are forecast to stay below 1800m. A slight clearing trend and continued cool temperatures is forecast for Wednesday with a few more flurries.

Snowpack Summary

Another 10-15cm Sunday night brings the recent snowfall to between 20-40cm. This new snow is generally bonding well with some isolated pockets of wind slab in the alpine. Below tree line the surface snow is moist on solar aspects. At tree line and above a 120cm+ firm slab with few weaknesses overlies weaker basal facets in much of the region.

Avalanche Summary

A few loose moist avalanches up to size 1.5 were observed out of steep solar alpine terrain on Monday near Lake Louise. Explosive control produced a couple size 1.5-2 slab avalanches in the recent storm snow with minimal propagation. Ski areas reported being able to ski cut small wind slabs from the recent snow up to size 1 that were running far.

Confidence

Intensity of incoming weather systems is uncertain on Tuesday

Problems

Deep Persistent Slabs

The snowpack is slowly gaining strength, but the weak basal facets continue to produce sudden collapse results and can produce large avalanches with large triggers. Stick to planar, supported slopes with a deeper snowpack if entering steep terrain.

Be aware of thin areas that may propogate to deeper instabilites.Pay attention to overhead hazards like cornices which could easily trigger deep slabs.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 4

Cornices

April is cornice failure season, and we continue to get reports of cornices failing and triggering deep slabs. Mature cornices can also break much further back than you expect, so give them a wide margin when traveling on ridges.

Do not travel on slopes that are exposed to cornices overhead.Stay well to the windward side of corniced ridges.

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 3

Loose Dry

Another 5-10cm of snow is forecast for Tuesday so we expect to see sluffing out of steep alpine and tree line terrain as this new snow arrives. We may also see a few small wind slabs near ridge crests so enter lee loaded terrain with caution.

Be cautious of sluffing in steep terrain, particularly where the debris flows into terrain traps.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Apr 11th, 2017 4:00PM