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Avalanche Forecast

Archived

Feb 28th, 2025–Mar 1st, 2025

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

Regions

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

Avoid exposing yourself to avalanche terrain or overhead hazards on Saturday. Upper elevations are heating up and very large natural avalanches are expected.

Confidence

Moderate

Avalanche Summary

A few more natural, remote, and explosives-triggered persistent slabs were observed Thursday, failing on the same late-January crust that caught a skier in a size 1.5 in Golden Tuesday and gave natural size 3 and 3.5 releases in the Dogtooth Range on Wednesday.

Size 2 and 3 deep persistent slabs were explosives-triggered on Wednesday, showing the basal snowpack reacting to large triggers.

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 potentially to mountaintop by Saturday afternoon. High overnight freezing levels mean crust recovery may be weak. This process is affecting 20 to 45 cm of settling recent snow, which has been redistributed 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

Friday Night

Clearing. 0 to 5 km/h southwest ridgetop wind. Freezing level remaining near 1800 m.

Saturday

Sunny. 5 to 10 km/h southwest ridgetop wind, up to 30 km/h in alpine. Freezing level rising to 2600 m. Treeline temperature 4 °C.

Sunday

Mainly sunny with cloud increasing. 0 to 5 km/h variable ridgetop wind. Freezing level 2000 m - 2500 m. Treeline temperature 4 °C.

Monday

Clearing after overnight flurries and up to 5 cm of snow above about 1700 m. 10 km/h northeast ridgetop wind. Freezing level 1700 m. Treeline temperature around 0 °C.

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 avalanche terrain; avalanches may run surprisingly far.
  • 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.