Avalanche Forecast

Issued: Apr 16th, 2017 4:00PM

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

tim haggarty, Parks Canada

Banff Yoho Kootenay.

Wind and storm slabs in the alpine continue to react to skier traffic today. The potential for heating keeps treeline hazard ratings at moderate over the next few days.

Summary

Weather Forecast

Clear skies will lead to a solid freeze overnight Sunday. Despite the potential for flurries Monday, freezing levels are still forecast to reach 2200m as unsettled air tracks east from the coast: don't rule out loose wet activity and light rain BTL. Tuesday should see West winds return to the moderate range with the potential for flurries.

Snowpack Summary

Sunday morning saw 5 to 10cm storm snow over recent crusts below 2300m. Solar heating is making new crusts today. 20-50cm of snow over the last week in the alpine sits over crusts on S aspects and was redistributed by moderate west winds. At tree line and above the mid-pack is a 120cm+ firm slab overlying weaker basal facets in much of the region.

Avalanche Summary

Skiers triggered a sz 2 slab at 2500m on the S aspect of Mt Jimmy Simpson 40 deep over a crust on a 30 degree slope. A field team on the Wapta reported sz 2 windslabs: 1 on the SE aspect of Mt Ayesha, and 2 on the East aspect of Arete Peak, an icefall triggered sz 2 slab off of the East aspect of Mt. Collie, and sz 1.5 loose wet off the S of Gordon

Confidence

Timing, track, or intensity of incoming weather system is uncertain on Monday

Problems

Wind Slabs

Moderate to strong west winds created fresh slabs and widespread wind effect in the alpine Friday redistributing up to 40 cm of recent snow. Use caution on solar slopes as well where this recent snow is bonding poorly to crusts.

If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.The recent snow may now be hiding windslabs that were easily visible before the snow fell.

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

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

1 - 2

Cornices

These saw rapid growth until winds died down Sunday morning. Minimize your time underneath these and remember that a cornice failure could also trigger the deep persistent slab on the basal facets.

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

Possible - Likely

Expected Size

1 - 3

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

Valid until: Apr 17th, 2017 4:00PM