Avalanche Forecast

Issued: Apr 19th, 2017 4:00PM

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

ian jackson, Parks Canada

Banff Yoho Kootenay.

Isolated windslabs exist at ridgetop on north and east aspects in the alpine but are generally small and predictable. Start and finish your trips early before the strong April sun destabilizes the snowpack.

Summary

Weather Forecast

Thursday looks to be partly cloudy with some afternoon flurries and freezing levels rising to ~ 2400m. Friday morning there will be a weak freeze, but sunny skies will make afternoon temperatures even warmer. Saturday looks to be the warmest day as we start to finally get into a springlike pattern. Winds look to be light through the period.

Snowpack Summary

The snowpack is a real mixed bag right now: totally dependent on aspect and elevation. At treeline and above, melt freeze crusts exist to ridgetop on solar aspects, while on north aspects, dry surface snow still exists above ~2200m. Below treeline the snowpack becomes wet through the day. The snowpack is slowly transitioning to a spring snowpack.

Avalanche Summary

Two size 3's were reported in the Sunshine Village backcountry. These were both initiated by cornice failures in the alpine at ~2800m which triggered the deep persistent weak layer and failed on the ground.

Confidence

Timing or intensity of solar radiation is uncertain on Thursday

Problems

Loose Wet

Afternoon warming will create loose wet problems at low elevations and on S and W facing terrain at higher elevations.

Pay attention to sluffing off cliffs and steep solar terrain, signs of a warming snowpack.

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

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

1 - 2

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 the deep persistent slab.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 4

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.

Cornices become weak with daytime heating, so travel early on exposed slopes.Give cornices a wide berth when travelling on or below ridges.

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

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

1 - 3

Valid until: Apr 20th, 2017 4:00PM