Avalanche Forecast

Archived

Apr 29th, 2023–Apr 30th, 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. Avoid all avalanche terrain. Avalanches will run to the valley bottom as the day heats up. Hikers should pay attention to avalanche warning signs at locations like Emerald Lake, Lake Louise and Sulphur Mountain.

Confidence

High

Avalanche Summary

A widespread natural and explosive triggered avalanche cycle up to size 3 occurred later in the afternoon on Friday and Saturday along with a skier-triggered size 2.5. Avalanches were a mix of wet loose, wet slabs, and deep persistent slabs, with many large avalanches running to the bottom of the runout zones.

Snowpack Summary

The heat is on! After a light refreeze overnight, sky-high freezing levels will melt and destabilize the snowpack early in the day. Expect wet snow on all solar aspects and unsupportive isothermal snow (slush) at lower elevations. The weak basal facets are a significant concern in thinner snowpack areas.

Weather Summary

Valley bottoms may cool to near freezing on Saturday night, but expect above-freezing temperatures at treeline and above with only radiative cooling overnight. Freezing levels will climb quickly on Sunday morning reaching ~3500 m. Alpine temperatures between +5 and +10°C are expected with strong solar input and light SW winds.

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.