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Avalanche Forecast

Archived

Apr 28th, 2023–Apr 29th, 2023

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.

Regions

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

A major avalanche cycle is underway and will last through to Monday. Avalanches will run to the valley bottom. Pay attention to avalanche warning signs at popular locations in the Emerald Lake and Lake Louise area and Sulphur mountain trail. Avoid all avalanche terrain and pass this message along to your hiking friends.

Confidence

High

Avalanche Summary

No significant avalanches were reported on Friday at 3:30 pm, but expect avalanches are occurring with treeline highs at +16C and still rising with intense solar input. The snow surface was frozen on Friday morning and was isothermal by 1:00 pm in thinner areas. Some size 1-2 wet loose avalanches were observed, one scrubbed to the ground, but the day's heat is now upon us until later this evening.

Snowpack Summary

The heat is on! Sky-high freezing levels will destabilize the snowpack early in the day, with no overnight refreezing expected for Friday through Monday. Expect wet, sloppy snow on all aspects and elevations and unsupportive isothermal snow (slush) at the treeline and below. We expect many large avalanches to fail on the ground.

Weather Summary

Friday night, valley bottoms may cool to near freezing, but treeline and above will not freeze, and temperatures may be up to +5C overnight. The avalanche hazard will increase early Saturday morning with freezing levels climbing to 3500 m, temperatures near 20C, strong solar input, and light wind. The same is expected for Sunday.

Terrain and Travel Advice

  • Avoid all avalanche terrain during periods of intense solar radiation.
  • Avoid exposure to overhead avalanche terrain as temperatures increase.

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.