Avalanche Forecast

Issued: May 3rd, 2017 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, Deep Persistent Slabs and Cornices.

Lisa Paulson, Parks Canada

Banff Yoho Kootenay.

Expect no overnight freeze for the next few days (freezing levels to 2800 m tonight and higher Thurs. night). Larger avalanches may occur with incoming hot weather - be mindful of terrain overhead. The hazard will quickly climb to HIGH on Thursday.

Summary

Weather Forecast

Freezing levels will rise to 3000m by tonight with no overnight recovery, rising through tomorrow to 3600m for Thursday night. Expect a mix of sun and showers with light to moderate SW wind for Thursday - Friday.

Snowpack Summary

Dry snow still exists on high north aspects. Moist surface snow and a variety of melt freeze crusts other aspects and elevations. Unsupportive isothermal conditions to 1900 m. A basal weakness remains at the bottom of the snow pack - reactive to large triggers but may wake up with the incoming warm weather, 2800 m freezing level, & solar input.

Avalanche Summary

Wind kept things cool most of the day, only some loose wet late to size 1.5 late in the day on S-W aspects in the alpine. This was caused by a combination of warm ambient air temperatures and rocks in the slope absorbing the sun's radiation and additionally heating the slope.

Confidence

Problems

Loose Wet

Loose wet avalanches can be expected on solar aspects in the afternoon when the day warms up.

If triggered the loose wet sluffs may step down to deeper layers resulting in large avalanches.Pay attention to sluffing off cliffs and steep solar terrain, signs of a warming snowpack.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 3

Deep Persistent Slabs

The weak basal facets can produce large avalanches with large triggers or heat. There will be no substantial recovery for the next few nights.

Pay attention to overhead hazards like cornices which could easily trigger the deep persistent slab.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

2 - 4

Cornices

Cornices are big this time of year and will fall off at some point in the next few weeks. They will be more frequent with the forecasted warming and solar effect over the next few days.

Cornices become weak with daytime heating, so travel early on exposed slopes.Pay attention to overhead hazards like cornices which could trigger the deep persistent slab.

Aspects: North, North East, East.

Elevations: Alpine.

Likelihood

Likely - Very Likely

Expected Size

2 - 3

Valid until: May 4th, 2017 4:00PM