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Avalanche Forecast

Archived

Feb 27th, 2025–Feb 28th, 2025

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

Regions

Purcells, Esplanade, Dogtooth, East Purcell, St. Mary, West Purcell.

The first deep persistent slabs of the warmup have been reported and there are likely many more to come. Time to dial down your exposure to avalanche terrain and overhead hazards to a minimum.

Confidence

Moderate

Avalanche Summary

Two size 3 deep persistent slabs and one size 2 were targeted with explosives near the Bugaboos Wednesday, evidence of the basal snowpack reacting to large triggers. The same mission produced shallower persistent slabs on the late-January crust, the layer that partially buried a skier in a size 1.5 in Golden on Tuesday and produced natural size 3 and 3.5 releases in the Dogtooth Range Wednesday. Activity of this type should resume or even intensify as warming continues.

Snowpack Summary

A melt-freeze crust moist or snow now glazes the surface on solar aspects and, by Friday, below about 1900 m. The depth of affected snow should increase over the coming days, but crust recovery may be weak. This process will affect 20 to 45 cm of settling recent snow, which has been affected by strong southwest winds at treeline and above. In shelter, it sits over a surface hoar or crust layer from mid-February.

Two more weak layers exist: a layer of facets, surface hoar, or crust from late-Jan buried 30 to 50 cm deep, and a layer of facets from early Dec, buried 70 to 120 cm deep. In many areas, facets or depth hoar also exist at the base of the snowpack. All of these layers are a concern as warming tests the snowpack.

Weather Summary

Thursday Night

Cloudy. 5 to 20 km/h west ridgetop wind, easing. Freezing level remaining near 1700 m.

Friday

A mix of sun and cloud. 0 to 5 km/h southwest ridgetop wind. Treeline temperature 4 °C. Freezing level to 2300 m.

Saturday

Mainly sunny. 5 to 10 km/h southwest ridgetop wind. Treeline temperature 4 °C. Freezing level 2500 m.

Sunday

Sunny. 0 to 5 km/h south west ridgetop wind. Treeline temperature 4 °C. Freezing level 2300 m - 2700 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Be aware of the potential for large, destructive avalanches due to deeply buried weak layers.
  • Avoid thin areas like rocky outcrops where you're most likely to trigger avalanches on deep weak layers.
  • Avoid exposure to overhead hazards when solar radiation is strong.
  • The likelihood of deep persistent slab avalanches will increase with each day of warm weather.

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.

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.

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.