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Avalanche Forecast

Archived

Apr 24th, 2023–Apr 25th, 2023

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Lizard-Flathead, South Rockies, Akamina, Flathead, Lizard, Moyie, Bull, Crowsnest North, Crowsnest South, Elkford East, Elkford West.

High daytime freezing levels and mild overnight temperatures will stress the snowpack, with the greatest concern for thin snowpack areas where buried crusts and weak layers may become reactive.

Stick to conservative, low-angle, and supported terrain features. Avoid overhead hazard during peak warming and sunshine.

Confidence

Moderate

Avalanche Summary

Observations are limited at this point in the season. If you have any observations, let us know what you are seeing through the Mountain Information Network.

Loose snow avalanches have been observed throughout the week as the sun weakens the surface snow.

Recent avalanche activity in adjacent forecast areas highlights the need to avoid rocky and thin snowpack areas for the remainder of the season. A fatal size 3 was reported from near Lake Louise on April 22nd, in a particularly thin and rocky area with a 50 cm deep snowpack. All information can be found here.

Snowpack Summary

Warm temperatures will weaken the surface snow as freezing levels rise on Tuesday, breaking down surface crusts and moistening any previously dry snow to around 2500 m on all aspects. Sun-affected terrain will see the most intense warming, likely creating wet and slushy snow to mountain top.

Around 20-40 cm deep, a thick melt-freeze crust is found up to 2200 m. As temperatures increase this will become a concern for avalanche activity.

The mid snowpack is generally settled and strong at treeline and above. The exception is areas where snow depths measure less than 150 cm. In these thin areas, the mid-pack is likely weaker and more faceted. These areas will respond more rapidly to warming temperatures, becoming unstable.

A weak layer of large, sugary crystals persists at the base of the snowpack. This layer is a concern as warming affects the snowpack - particularly in thin and rocky snowpack areas.

Weather Summary

Monday Night

Mostly cloudy. Light westerly wind. Freezing levels drop to 1700 m. Flurries possible.

Tuesday

Mostly sunny with freezing levels rising to 2500 m. Treeline temperatures around +7 °C. Moderate westerly winds. No snowfall.

Wednesday

Mostly sunny with freezing levels rising to 2800 m. Treeline temperatures of +10 °C. Moderate westerly winds.

Thursday

Full sun with freezing levels heading towards 3000 m. Treeline temperatures above +10 °C. Light westerly winds.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Back off slopes as the surface becomes moist or wet with rising temperatures.
  • 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

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

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.