Avalanche Forecast

Issued: Apr 17th, 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.

Lisa Paulson, Parks Canada

Banff Yoho Kootenay.

Light flurries and cooler weather for Tuesday. Snow amounts received may vary across the region.

Summary

Weather Forecast

Freezing levels will drop to valley bottom through the night as showers and flurries move into the region. Moderate West winds follow they system. Clearer skies for later in the week.

Snowpack Summary

A thin breakable melt freeze crust now caps the 20-50cm of snow from last week on all aspects expect due North above 2300 m. Stubborn windslabs may be found on Northerly aspects in the high alpine. At tree line and above the mid-pack is a 120cm+ firm slab overlying weaker basal facets in much of the region.

Avalanche Summary

No new avalanches reported today. On Sunday: 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. Also late Sunday in the heat of the day, two size 3's and one size 2 from thin snowpack areas (lookers right of isolated col), SW aspect, 2500 m, wide propagations, slid on ground.

Confidence

Problems

Wind Slabs

The windslabs created on Friday by moderate West wind is now capped with a thin melt freeze crust on all aspects except due North. Prior to the new surface crust, these slabs were failing on an older crust 40 cm down on solar aspects.

If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 2

Cornices

Cornices continue to fail. Minimize your time underneath these and remember that a cornice failure could also trigger the deep persistent slab on the basal facets.

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

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.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 4

Valid until: Apr 18th, 2017 4:00PM