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Avalanche Forecast

Archived

Mar 16th, 2023–Mar 17th, 2023

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Banff Yoho Kootenay, Banff, East Side 93N, Kootenay, Lake Louise, LLSA, Sunshine, West Side 93N, Field.

We're doing avalanche control on Mt. Whymper, Friday March 17. Please avoid recreating in the Mt. Whymper avalanche control area. Click the LINK for location details.

Thank you.

Confidence

Moderate

Avalanche Summary

We've had numerous reports of skier triggered avalanches in the last 36h. Ranging in size from 2-3, failing in the basal facets. These avalanches have largely been triggered from thin areas in the snowpack.

There have been multiple reports of natural avalanches, up to size 3, also failing in the basal facets. Mt. Norquay ski hill also reported a size 4 avalanche on Mt. Brewster in the last 48h.

As the afternoons warm up, we are expecting to see continued activity on these persistent weak layers.

Snowpack Summary

15-30 cm's of recent snow has fallen on a freshly buried (March 12) layer of surface hoar, facets and sun crust. Snow profiles are producing sudden results on this layer. Sun crusts at or near the surface have been reported in isolated areas below 1600m. The mid-pack comprises various Jan crust's that are now down 60-100 cm. The weak Nov. 16 basal facet layer is down 50-120 cm producing sudden results in snowpack tests. The basal facets have become more triggerable with the additional load and warmth. Cornices are also quite large and will also be affected by solar inputs.

Weather Summary

The high pressure that we have been experiencing will stick around through Friday and into the weekend, with mainly sunny skies persisting.

Friday's alpine high will be -10 and valley bottoms will be as warm as +5, with freezing levels set at 1800m. Winds will continue to be light in the morning, but will creep up to 40 km/h by the afternoon out of the south/southwest.

Saturdays weather looks to be quite similar, however temperatures could be even warmer.

For a more detailed forecast click here.

Terrain and Travel Advice

  • Uncertainty is best managed through conservative terrain choices at this time.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.