Avalanche Forecast

Issued: Mar 6th, 2017 4:00PM

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

grant statham, Parks Canada

Banff Yoho Kootenay.

We are surprised by the size of the avalanches that occurred from avalanche control on Sunday and Monday - up to 400m propagations! More avalanche control planned for Tuesday on Mt. Whymper and Simpson - no skiing or climbing in these areas please.

Summary

Weather Forecast

Overcast skies with light precipitation for Tuesday, but no measurable accumulation expected. Temperatures will remain cool, ranging from -12 to -18 and expect winds straight out of the west at about 30-40 km/hr in alpine areas. A bit more snow expected for Wednesday.

Snowpack Summary

40cm of storm snow has developed into a touchy storm slab that is very sensitive to triggers at treeline and above. This sits over a supportive mid-pack, with the lower half of the snowpack consisting of weak facets and depth hoar. There is isolated wind effect near ridge crests only; the notable observation is the lack of wind effect.

Avalanche Summary

Avalanche control on Mt. Bosworth today (near Lake O'Hara) resulted in widespread fracture propagations (up to 400m)that released very easily. The ease and speed of the fractures was surprising; most avalanches occurred in the recent storm snow and one size 3 released on the Dec 19 facets. Lots of storm slab avalanches observed in the backcountry.

Confidence

Due to the number of field observations

Problems

Storm Slabs

A 50 cm slab of storm snow is touchy and very sensitive to triggers. Avoid any avalanche starting zones, as this slab appears to be widespread. Fracture lines have been spreading into adjacent terrain, so mind your exposure carefully.

Be aware of the potential for wide propagations.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Deep Persistent Slabs

The entire upper half of the snowpack overlies a structurally weak base. Avoid thin parts of a slope or rocky outcrops at tree line and above. where triggering of this problem is most likely.

Be aware of thin areas that may propogate to deeper instabilites.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 3

Valid until: Mar 7th, 2017 4:00PM