Avalanche Forecast

Issued: Apr 21st, 2018 4:00PM

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

conrad janzen, Parks Canada

Banff Yoho Kootenay.

The new snow should improve the ski quality for Sunday but watch for wind loaded pockets at higher elevations. Start and finish early to take advantage of the lower hazard during the cooler parts of the day, and enjoy the spring skiing!

Summary

Weather Forecast

Cool temperatures and a few flurries are forecast for Sunday. Alpine winds will start out in the Moderate range from the West and slowly diminish during the day. Skies will clear later in the day Sunday as the high pressure system moves in and we get set for the next few days of clear skies and increasing temperatures.

Snowpack Summary

5-10cm of snow with very strong SW winds on Saturday has formed new wind slabs above treeline. Buried temperature crusts exist to 2000m on all aspects and to ridge tops on solar slopes, including the Mar 15 sun crust down 40-70 cm in the alpine. Moist snow at lower elevations, with the entire snowpack becoming moist near valley bottom.

Avalanche Summary

Limited observations on Saturday with some thin new surface slabs reactive to ski cutting in steep lee areas. Lots of loose wet avalanche activity on steep solar aspects in the past several days when the sun was out. Explosive control at Sunshine produced one size 2.5 cornice failure on Friday.

Confidence

Problems

Wind Slabs

New wind slabs from Saturday will likely be reactive to skier traffic in lee areas on Sunday. The buried winds slabs from the previous week are losing sensitivity, but may still be present in isolated alpine locations.

Be careful with wind loaded pockets, especially near ridge crests and roll-overs.The recent snow may now be hiding windslabs that were easily visible before the snow fell.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Loose Wet

Temperatures should remain fairly cool on Sunday, but if the sun does come out watch for rapid warming of the surface snow and solar triggered sluffing as a result of this.

Use extra caution on slopes if the snow is moist or wet.Watch for clues, like sluffing off of cliffs, that the snowpack is warming up.

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

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

1 - 2

Persistent Slabs

Not much activity on this, but a few avalanches last week were deeper than the majority. Some of these clearly stepped down to the March 15 crust on solar aspects. On shaded aspects these were likely sliding on facets formed at the same interface.

Avoid shallow snowpack areas where triggering is more likely.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

1.5 - 2.5

Valid until: Apr 22nd, 2018 4:00PM