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Avalanche Forecast

Archived

Apr 26th, 2023–Apr 27th, 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 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

Cariboos, Kootenay Boundary, Lizard-Flathead, North Columbia, North Rockies, Purcells, South Columbia, South Rockies, Glacier, Blue River, Clearwater, McBride, Premier, Quesnel, Sugarbowl, Bonnington, Grohman, Kootenay Pass, Norns, Rossland, South Okanagan, Ymir, Akamina, Flathead, Lizard, Clemina, Esplanade, Jordan, North Monashee, North Selkirk, Shuswap, Kakwa, McGregor, Pine Pass, Renshaw, Robson, Tumbler, Dogtooth, East Purcell, Moyie, St. Mary, West Purcell, Badshot-Battle, Central Selkirk, Goat, Gold, Kokanee, North Okanagan, Retallack, Valhalla, Whatshan, Bull, Crowsnest North, Crowsnest South, Elkford East, Elkford West.

Rising temperatures will increase the avalanche danger and potentially trigger very large avalanches. Read more in this Forecasters' Blog.

Confidence

Moderate

Avalanche Summary

Recent observations are limited to small wet loose avalanches on sun-exposed slopes. Starting Thursday we expect rapid warming to cause a natural cycle of wet avalanches and cornice failures as well as the potential for very large persistent and deep persistent slab avalanches.

Snowpack Summary

Moist surfaces can be expected everywhere except the highest north-facing slopes.

The sudden addition of heat to the snowpack has potential to reawaken 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. The Purcells likely require minimal heat to trigger large avalanches, while other parts of the interior have been experiencing a period of dormancy and may take longer to react to the warming.

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

Weather Summary

Thursday

A high pressure ridge is bringing mostly sunny skies (except partly cloudy in the Cariboos and North Rockies) with freezing levels climbing to 2500 m in southeastern BC and 2000 m in the North Rockies.

Friday

Sunny with freezing levels sustained at 3500 m in southeastern BC and 2500 m in the North Rockies.

Saturday

Sunny with freezing levels sustained at 3500 m in southeastern BC and 3000 m in the North Rockies.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Avoid steep slopes when air temperatures are warm, or solar radiation is strong.
  • 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.