Avalanche Forecast

Archived

Apr 27th, 2023–Apr 28th, 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 will begin on Friday and last through the weekend. Avoid all avalanche terrain and pass this message along to your friends who go hiking. Avalanches will run to the valley bottom. Mt. Stephen, Mt. Field, Mt. Cathedral and Mt. Hector avalanche zones are closed on Friday for avalanche control.

Confidence

Moderate

Avalanche Summary

No significant avalanches were reported on Thursday as of 3:00 pm. The snow surface was frozen on Thursday morning and was isothermal by 1:00 pm. Some small wet loose sluffs were observed, but the heat of the day is upon us now until later this evening.

Snowpack Summary

The weak snowpack we've been warning about all winter is about to get a major test, as sky-high freezing levels will destabilize the snowpack during the day, with no refreezing expected overnight for Saturday and Sunday. Expect wet, sloppy snow on all aspects and elevations and isothermal snow (slush) at the treeline and below. We expect many large avalanches to fail on the ground.

Weather Summary

A ridge of high pressure establishes itself over the region today, bringing the first hot period of spring. Freezing levels on Saturday could reach up to 3500 m with sunny skies. Valley bottom high temperatures will reach 17 degrees on Friday and 20 degrees on Saturday. Major change underway.

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.