Avalanche Forecast

Archived

Apr 25th, 2023–Apr 26th, 2023

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Below Threshold.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Below Threshold.

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, Banff, East Side 93N, Kootenay, Lake Louise, LLSA, Sunshine, West Side 93N, Field.

Start and finish early to take advantage of better travel and a lower likelihood of upper snowpack avalanches while the surface snow remains frozen. Also, keep the deep persistent slab in mind as this remains a concern and can be triggered regardless of surface snow conditions.

Confidence

Moderate

Avalanche Summary

Some small loose wet avalanches have been observed in the past few days on steep solar aspects or at low elevations with daytime warming. A size 3 skier-triggered avalanche failing on the basal facets occurred in a closed area within the Lake Louise ski resort on Saturday.

Snowpack Summary

1-4 cm new snow. Solar aspects are getting moist in the afternoon, creating new crusts daily, and multiple buried crusts are present. On northerly aspects, temperature crusts are present up to 2200 m, with 10-20 cm of preserved surface snow above this elevation and some wind transport at ridge crests. The base of the snowpack remains weak due to the presence of facets and depth hoar.

Weather Summary

Some clearing tonight, followed by building clouds and flurries or rain below 2100 m on Wednesday. Winds will increase to WSW strong. Afternoon freezing levels will climb further to 23-2500 m. Freezing levels will fall to the valley bottom at night.

Thursday, skies clear, winds diminish, and solar input becomes more of a factor.

Towards the weekend, temperatures climb with strong solar input and little to no overnight recovery.

Terrain and Travel Advice

A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.

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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

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.