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Avalanche Forecast

Archived

Feb 28th, 2025–Mar 1st, 2025

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

Regions

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

Conditions are tricky now, given recent extreme winds, persistent weak layers, warm temperatures and sun. See the Special Avalanche Warning (SPAW) above for more details.

The Mt. Whymper intermittent closure zone will be closed on Saturday, March 1 for avalanche control. No backcountry activities in this area for the day.

Confidence

High

Avalanche Summary

Some natural activity in the backcountry of both Lake Louise and Sunshine ski hills up to size 2.5. A size 2.5 in the National Goegraphics bowl of the Lake Louise backcountry (see photo) went 60cm deep on the Jan 30th layer, likely triggered by warmth and sun. Natural activity was also noted to size 3 on Mount Whymper in past 24 hours.

On Thursday, helicopter avalanche control on Mt. Field, Stephen, and Dennis produced slab avalanches up to size 3.

Snowpack Summary

Winds in alpine and treeline areas have blown 10 - 30cm of snow from last weekend. This snow sits over previous slabs and is now up to 60cm thick. The slabs sit on weak layers of facets, surface hoar or sun crust formed in late Jan and Feb.

The mid-pack is generally faceted, while depth hoar and crusts form an even weaker base. The snowpack is the weakest in eastern areas where snow depths are low. In these areas, the basal weaknesses should be carefully considered.

Weather Summary

Saturday - Freezing levels up to 2500m, light winds and no snow.

Sunday - much the same

Monday - an upslope storm may bring 5cm in the East, and minimal to the West

Terrain and Travel Advice

  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and slopes above cliffs.
  • Avoid steep, sun-exposed slopes when the air temperature is warm or when solar radiation is strong.
  • Watch for newly formed and reactive wind slabs as you transition into wind-affected terrain.

Problems

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.

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.

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.