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Avalanche Forecast

Archived

Mar 18th, 2023–Mar 19th, 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.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely.

Regions

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

After a week full of avalanche activity: Factor in the effects of rising freezing levels and solar inputs as you select your objectives this weekend.

The avalanche problems described will become more sensitive to human triggering as the snowpack warms up and the potential will increase for snow to move as cornice failures or small solar triggered events which could initiate these slabs as well.

Confidence

Moderate

Avalanche Summary

Since the latest storm, we have seen avalanches almost every day failing on the deep persistent layers.

See the other bulletin for the region for Saturday's avalanche control results in Yoho NP.

Friday avalanche control on Mt Whymper produced avalanches with every shot: Small slab results were observed with the March 12 Persistent Layer. Large slabs to sz 3 were observed on the Deep Persistent Layer, several of which initiated directly to the base of the snowpack. Finally, several pockets: slabs to sz 2 in themselves, were sympathetically triggered by other avalanches in motion on SW facing features. These were initiating on the January Persistent Layer of crusts.

Snowpack Summary

15-25 cm of snow buried a layer of surface hoar, facets and sun crust on March 12. Suncrusts are forming on steep solar slopes.

The midpack comprises various Jan crust layers that are now down 40-110 cm.

The weak Nov. 16 basal facet layer is down 50-130 cm producing sudden results in snowpack tests.

Weather Summary

The region will continue to sit under the influence of a high pressure system until late on Sunday. Heating will be the most significant weather influence to the snowpack for the period.

Sunday, the winds should be very light. Freezing levels will reach to near 2000m and solar heating may bring temperatures to peak values, however, as the ridge breaks down some convective activity can be expected in the afternoon which may curb heating. Overnight, a trough will bring increasing cloud cover and flurries.

Monday up to 5cm of snow may be possible with freezing levels reaching to about 1600m.

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

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.

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.