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Avalanche Forecast

Archived

Dec 19th, 2025–Dec 20th, 2025

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

Regions

Purcells, Crawford, East Purcell, St. Mary.

Up to 50 cm of recent snow and strong southwest winds continue to form wind slabs reactive to human triggers.

Make conservative terrain choices and avoid overhead hazard.

Confidence

Moderate

  • Uncertainty is due to the limited number of field observations.

Avalanche Summary

On Thursday, a naturally triggered size 2.5 wind slab avalanche was reported on a northeast aspect in the alpine.

On Wednesday, numerous natural and explosive triggered storm slab avalanches up to size 2 were reported primarily on north and easterly aspects at treeline and above.

Snowpack Summary

30-50 cm of recent snow and strong southwest winds have formed slabs that will be most reactive in wind affected terrain. This recent snow overlies a 3 to 5 cm thick crust below 2200 m.

90 to 170 cm down is a weak layer of faceted snow at higher elevations or surface hoar in sheltered terrain.

100 to 180 cm down is a prominent crust which may have facets above or below.

Depth hoar(large facets) can be found at the bottom of the snowpack.

Weather Summary

Friday Night
Mostly cloudy with isolated flurries. 0 to 5 cm of snow. 30 km/h southwest ridgetop wind. Treeline temperature -9 °C. Freezing level valley bottom.

Saturday
Mostly cloudy with flurries. 5 to 10 cm of snow. 30 km/h southwest ridgetop wind. Treeline temperature -9 °C. Freezing level valley bottom.

Sunday
Mostly cloudy. 35 km/h south ridgetop wind. Treeline temperature -7 °C. Freezing level valley bottom.

Monday
Mix of sun and clouds. 30 km/h southwest ridgetop wind. Treeline temperature -6 °C. Freezing level valley bottom.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Make conservative terrain choices and avoid overhead hazard.
  • Watch for newly formed and reactive wind slabs as you transition into wind-affected terrain.
  • Keep your guard up at all elevations. Wind slab formation has been extensive and could extend into openings below treeline.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.

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.