Avalanche Forecast

Issued: Apr 20th, 2018 4:00PM

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

stephen holeczi, Parks Canada

Little Yoho.

Expect a poor freeze below 2000m Saturday, and some new wind slabs up high. We will be switching to "spring conditions" over the next couple of days. The coming week looks to be a warm one.

Summary

Weather Forecast

10-15cm is expected in Little Yoho Saturday with Strong SW winds with the potential for light rain at valley bottom. There will be a poor freeze below 2000m but temperatures should cool slightly in the afternoon with the passage of a cold front. A dramatic warmup is expected next week.

Snowpack Summary

Up to 50 cm of storm snow near the divide affected by strong SW winds Tuesday evening. Several buried temperature crusts exist to 2000m on all aspects and to ridge tops on solar slopes, including the Mar 15 sun crust down 35-50 cm in the alpine. Moist snow at lower elevations, with the entire snowpack becoming moist near valley bottom.

Avalanche Summary

Avalanche control yesterday produced mainly wind slabs in the sz 2 range 20-50cm deep with decent propagations up to 50m wide. Several of these events entrained more mass as they moist snow at lower elevations. Large loose wet avalanches were seen on both Mts Stephen and Field today to sz 3.

Confidence

Freezing levels are uncertain on Friday

Problems

Wind Slabs

20-50 cm of storm snow has fallen over the past few days with the greater amounts near the divide. Increased SW wind Tuesday afternoon loaded lee terrain. New snow with strong winds will add to this problem in the short term.

Be careful with wind loaded pockets, especially near ridge crests and roll-overs.Use caution in lee areas in the alpine and treeline. Storm snow is forming touchy slabs.

Aspects: North, North East, East.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2.5

Loose Wet

Sun likely will not be a major issue Saturday, but rain is possible at lower elevations. With a poor freeze, this could cause some natural activity in steep below treeline terrain.

Use extra caution on slopes if the snow is moist or wet.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

A few of the avalanches seen over the last two days were deeper than the rest. We suspect that the both facets and crust on the March 15 interface were to blame. Good to bear in mind for coming warm periods.

Be cautious with convexities and steep slopes on solar aspects.Avoid shallow snowpack areas where triggering is more likely.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

1 - 2.5

Valid until: Apr 21st, 2018 4:00PM