Avalanche Forecast

Issued: Apr 15th, 2017 4:00PM

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

conrad janzen, Parks Canada

Banff Yoho Kootenay.

New wind slabs will remain easy to trigger for the next day or so until the winds ease and the new snow has a chance to bond. Sunday and Monday should allow for good travel and ski conditions but pay attention to daytime heating as the skies clear.

Summary

Weather Forecast

Moderate to strong west winds with light snowfall will continue through Saturday night before easing up on Sunday morning. Freezing levels will creep higher Sunday and higher still Monday with increasing solar influence as a ridge and clearing skies arrives on Sunday afternoon.

Snowpack Summary

5cm of new snow over a melt freeze crust on all aspects at tree line, and up to 2900m on solar aspects. 20-50cm of snow over the last week in the alpine with moderate west winds creating soft slabs and rapid cornice growth. At tree line and above the mid-pack is a 120cm+ firm slab overlying weaker basal facets in much of the region.

Avalanche Summary

Reports of a couple skier triggered wind slabs in the alpine at Bow Summit and Cathedral Peak on Friday as the winds increased. Propagation up to 100m was reported. On Saturday local ski areas were seeing rapid cornice growth and were able to ski cut small wind slabs in lee areas throughout the day. No new naturals observed but visibility was poor.

Confidence

Timing of incoming weather systems is uncertain on Tuesday

Problems

Wind Slabs

Moderate to strong west winds with new snow have created soft slabs in the alpine. Skier triggering will remain likely through Sunday. Use caution if entering steep lee loaded areas and expect sluffing in steep gullies until the winds ease off.

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.

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

1 - 2

Cornices

Moderate to strong west winds have been rapidly building cornices over the past two days. 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 16th, 2017 4:00PM