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Avalanche Forecast

Archived

May 4th, 2023–May 5th, 2023

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
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

Kootenay Boundary, Bonnington, Kootenay Pass, Norns, Rossland, South Okanagan, Ymir, Moyie.

Rain will continue to rapidly destabilize the snowpack, increasing the likelihood of large avalanches. Read more in the Forecasters' Blog.

Confidence

Moderate

Avalanche Summary

An avalanche cycle of large to very large (size 2 to 4) wet loose and slab avalanches, cornice failures, and deep persistent slab avalanches continues over much of the region. We expect this cycle will continue over the coming days as rain soaks the snowpack.

Snowpack Summary

Rain will continue to wet the snowpack.

The intense addition of heat to the snowpack is reawakening dormant weak layers, including weak snow above crusts buried in late March (50 to 100 cm deep) and the weak basal facets found at the bottom of the snowpack. The timing of when and where persistent slabs will reawaken is uncertain, but will increase with each day of warming.

The snowpack is diminishing below treeline, but persistent and deep persistent slab avalanches could release at higher elevations and run into valley bottoms.

Weather Summary

A trough of low pressure will bring cloudy skies with 10 to 20 mm of rain and a freezing level near 3000 m for Friday. Precipitation continues into the weekend with a freezing level decline to 2000 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Travel in alpine terrain is not recommended.
  • Minimize exposure during periods of heavy loading from rain.
  • Minimize exposure to overhead avalanche terrain, large avalanches may reach the end of runout zones.
  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
  • The more the snowpack warms-up and weakens, the more conservative you`ll want to be with your terrain selection.
  • The likelihood of deep persistent slab avalanches will increase with each day of warm weather.

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.

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.

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.