Avalanche Forecast

Issued: Feb 4th, 2019 5:18PM

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

william lawson, Parks Canada

Banff Yoho Kootenay.

Increased reactivity of the Jan 17 surface hoar/crust layer is due to recent loading of storm snow. Distribution is spotty, so dig down to verify if this layer is present in your local area.

Summary

Weather Forecast

A arctic ridge of high pressure will linger in the bulletin region for the remainder of the week. Temperatures will remain frigid, with evening lows down to -30. A temperature inversion has set in at higher elevations. Light winds, sunny skies and temperatures in the low negative teens will make the alpine the place to be.

Snowpack Summary

Recent snow and wind have created wind slab on lee alpine slopes. At treeline elevations, up to 65cm of snow sits over the Jan.17 surface hoar. In shallower areas weak facets and depth hoar exist below the Dec 10 interface. In deeper snow packs this basal weaknesses is less pronounced.

Avalanche Summary

No new avalanches reported or observed today. Evidence of a widespread natural avalanche cycle to size 2.5 from the weekend is visible at tree line and above. Recent reports have noted skier triggered avalanches to size 1.5 on the Jan 17 SH layer. As the recent storm snow continues to settle we can expect larger propagations on this weak layer.

Confidence

Problems

Wind Slabs

Recent winds have redistributing the storm snow in the alpine and created fresh windslabs in lee areas. These slabs could be up to 70cm deep.

Use caution in lee areas. Recent wind loading have created wind slabs.

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

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

1 - 2.5

Persistent Slabs

The Jan 17 layer is a combination of Surface Hoar and/or a melt freeze crust. Since the recent storm, it has become reactive to skier traffic and can generally be found down 50cm. Dig down, look and test this layer at tree line and below.

Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2.5

Deep Persistent Slabs

The new snow load may start waking up the deep persistent facet weakness down 80-160 cm. This is of greatest concern in shallow snowpack areas where the basal facets are weakest.

Avoid thin, rocky or unsupported slopes.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Valid until: Feb 5th, 2019 4:00PM