Avalanche Forecast

Issued: Apr 19th, 2018 5:33PM

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

tim haggarty, Parks Canada

Banff Yoho Kootenay.

Solar heating over the last two days resulted in a widespread avalanche cycle up to sz 3 with some events running full path. Windslabs in the alpine and loose wet avalanches at lower elevations will remain a concern into the weekend.

Summary

Weather Forecast

While skies do not look as clear for Friday, freezing levels are forecast to be a bit higher and some sunny periods should be expected. West winds will be increasing in the alpine through Friday into the strong range for Saturday as a pacific system brings up to 8cm of snow with a freezing level around 2000m.

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 today produced mainly windlslabs 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. During flights, evidence of a natural cycle to sz 3 could be seen in the Banff region mainly Ne facing windslabs from the last 36 hrs.

Confidence

Freezing levels are uncertain on Friday

Problems

Loose Wet

Solar inputs over the last two days have resulted in mainly small loose wet events at upper elevations but all avalanches have been picking up mass gaining size quickly as they reach the moist snow around treeline.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 2

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 creating reactive windslabs.

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

Aspects: North, North East, East.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2.5

Persistent Slabs

A few avalanches in the last two days were much deeper than the majority. Some of these clearly stepped down to the March 15 crust and on shaded aspects were likely sliding on facets associated with the same burial date

Avoid shallow snowpack areas where triggering is more likely.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

1.5 - 3

Valid until: Apr 20th, 2018 4:00PM