Avalanche Forecast

Issued: Apr 17th, 2015 4:00PM

The alpine rating is below threshold, the treeline rating is below threshold, and the below treeline rating is below threshold. Known problems include Loose Wet, Cornices and Wind Slabs.

conrad janzen, Parks Canada

Banff Yoho Kootenay.

We are gradually moving into true spring melt- freeze conditions although higher N facing terrain still has a winter snowpack. Start early, minimize exposure to steep solar aspects later in the afternoon, and enjoy the fast travel.

Summary

Weather Forecast

Winds are forecast to switch to the North and calm down on Friday night as a ridge of high pressure begins to build. No new precipitation is expected on Saturday or Sunday. Freezing levels should start at valley bottom overnight but rise to 2200m on Saturday and 2300m on Sunday. Early starts and finishes will be important.

Snowpack Summary

Moist snow up to 2100m on all aspects and to ridge top on all solar aspects. Lots of wind effect in alpine areas. Recent wind slabs are beginning to bond but may still be an issue at higher elevations. Cornices are a major concern with the winds and warm temperatures. Recent cornice failures have triggered the basal facets in several locations.

Avalanche Summary

Wet loose natural avalanches up to size 2 were seen Friday afternoon with the warm temperatures. Isolated whumpfing was still noted in the Observation Sub Peak area Thursday and was likely due to new wind slabs sitting over sun crust. On Wednesday, a large cornice release triggered a size 3 avalanche on the basal facets in the Sunshine backcountry.

Confidence

Problems

Loose Wet

Expect an increase in solar triggered avalanche activity with daytime heating over the weekend. It is possible that wet slides could trigger the basal facet layers if they have enough mass. Start early and be off steep solar aspects by midday.

Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.

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

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 2

Cornices

Many large cornices have formed recently, and there have been numerous reports of cornice failures over the last week. In isolated events these have been big enough to trigger the deep basal facets.

Cornices become weak with daytime heating, so travel early on exposed slopes.Extra caution needed around cornices with current conditions.

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 3

Wind Slabs

Wind slabs are becoming less reactive, but watch for how these are bonding to the harder surfaces below especially on high N aspects.

Be careful with wind loaded pockets, especially near ridge crests and roll-overs.

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

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

1 - 2

Valid until: Apr 18th, 2015 4:00PM