Avalanche Forecast

Archived

Apr 23rd, 2023–Apr 24th, 2023

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Below Threshold.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Below Threshold.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Below Threshold.

Regions

Jasper, Brazeau, Churchill, Cirrus-Wilson, Fryatt, Icefields, Maligne, Marmot, Miette Lake, Pyramid.

Sunday night is expected to have less of an overnight freeze than previous nights and Monday may start warm. The thick high clouds potentially will hold onto the warm air overnight. If Monday starts warm, this could increase the reactivity of cornices and deep persistent slabs.

Confidence

Moderate

Avalanche Summary

There was an avalanche Fatality in Banff Park near Lake Louise Saturday from a deep large human triggered slide. On Friday, 2 natural large deep avalanches were observed, both on East aspect in the alpine triggered by a cornice failure.

Maligne road patrol saw no new natural avalanche activity on Friday.

Post avalanche observations to the MIN.

Snowpack Summary

10cm of new snow from last week has settled onto sun crusts on solar aspects with a melt-freeze crust below tree line. Old wind slab is on exposed alpine terrain.

A weak layer of sun crust or facets lingers in the mid-pack but the main concern is the depth hoar and basal facets at the bottom of the snowpack causing our deep persistent slab problem.

Weather Summary

Parkers ridge weather on Monday will bring sun and cloud, no new snow, high of 1 °C, light winds, and 2400m freezing level. Tuesday will have sun with flurries, -5 °C in the morning then a high of -2 °C, gusting 35 km/h winds, and 1900m freezing level. Wednesday will be sun and cloud, -7 to 0 °C, light winds, and 2200m freezing level.

Terrain and Travel Advice

Cornices become weak with daytime heating.
In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.
Avoid exposure to slopes that have cornices overhead.

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.