Avalanche Forecast

Issued: Apr 18th, 2014 4:00PM

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

Lisa Paulson, Parks Canada

Banff Yoho Kootenay.

Freezing levels could climb to as high as 2500 m over the weekend. Watch for increased loose snow avalanches with wind gusts and solar affect. Get a very early start - Best skiing will be above treeline on North aspects.

Summary

Weather Forecast

Freezing levels to valley bottom tonight, mainly cloudy & clearing by morning.Â Expect clear skies Saturday morning, winds will be gusty, with convective flurries in the afternoon.Â Freezing levels on Saturday night rise to 2500 m.Â Sunday morning, some sunny breaks, gusty wind through the day, and afternoon cloud build up.

Snowpack Summary

Up to 30 cm so far, snow will taper off this evening. A supportive melt-freeze crust exists on all aspects to 2100m & higher on S and W aspects. The basal layer may become more active over the coming days with intense solar radiation or warming temps or if you trigger the weak spot, as demonstrated 2 days ago on Mt. Whymper, (see avalanche table).

Avalanche Summary

Earlier this week a there was a size 3.5 skier remote avalanche on the basal facets on Mt. Whymper. The group heard a whumph and 30 seconds later the slide released taking out the whole slope the party had just climbed up from 70m away. Picture.Today - only loose sloughing off cliff features and a size 2 on a W aspect, from rocks, along Hwy 93N.

Confidence

Problems

Deep Persistent Slabs

The basal layer is still prominent in thin and variable areas. It is well bridged and is unlikely to be triggered, but consequences could be large if you hit the right spot. With warmer temps & sun affect it may become more sensitive to triggering.

Be aware of the potential for full depth avalanches due to deeply buried weak layers.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

1 - 3

Loose Dry

Watch for an increase loose dry avalanches off cliffs with forecasted gusty winds and solar affect.

Watch for clues, like sluffing off of cliffs, that the snowpack is warming up.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 2

Loose Wet

Watch for loose wet avalanches being triggered by sun affect, potentially initiating from cliffs/rocks above, entraining the recent storm snow, and sliding on underlying crusts.

Start and finish early before the surface crusts melt.

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Apr 19th, 2014 4:00PM