Avalanche Forecast

Issued: Apr 14th, 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 Wind Slabs.

Tim Haggarty, Parks Canada

Banff Yoho Kootenay.

West winds have created touchy new windslabs. There is the potential for more snow in some parts of the region Saturday. This, coupled with increasing winds will raise the hazard this weekend.

Summary

Weather Forecast

West winds will continue to build late Friday reaching strong values midday Saturday before diminishing Sunday. Up to 15cm of precip is in the forecast for the 93N with less further South for Saturday. Freezing levels look to stay around 1500m for Saturday but will creep higher Sunday and higher still Monday with increasing solar influence.

Snowpack Summary

Small amounts of snow over this past week have added up to about 20-40cm that moderate west winds redistributed Thursday night. A new crust formed to 2300m on North aspects late Thursday and much higher on sunny slopes. At treeline and above, the midpack is a 120cm+ firm slab with few weaknesses overlying weaker basal facets in much of the region.

Avalanche Summary

Late day heating Thursday may have triggered two sz 2.5 storm slabs near the Lake Louise resort 60cm x 100m wide. West winds overnight resulted in several skier triggered windslabs propagating up to 100m wide in the alpine. Skiers deliberately triggered a sz 2 windslab at the top of the North gulley on Mt Cathedral.

Confidence

Intensity of incoming weather systems is uncertain on Saturday

Problems

Deep Persistent Slabs

The snowpack is 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

West winds will add fragile new growth to the mature cornices that exist throughout the range. These are a fall hazard while traveling on ridges and a significant overheard hazard to travelers below them. Wind, warm temps or sun may cause failures.

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, South.

Elevations: Alpine.

Likelihood

Likely

Expected Size

1 - 3

Wind Slabs

Up to 40cm of recent snow has been available to transport by West winds. Skiers could easily trigger windslabs local to ridges Friday. With more wind and more snow in the forecast, expect these slabs to remain touchy through Sunday.

Minimize overhead exposure during periods of heavy loading from new snow, wind.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

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

Elevations: Alpine.

Likelihood

Likely - Very Likely

Expected Size

1 - 3

Valid until: Apr 15th, 2017 4:00PM