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Avalanche Forecast

Archived

Dec 17th, 2025–Dec 18th, 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 unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
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

East Purcell.

Up to 35 cm of new snow and southwest winds have formed fresh storm slabs that will be most reactive in wind affected terrain.

Make conservative terrain choices and avoid overhead hazard.

Confidence

Moderate

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

Avalanche Summary

On Tuesday, numerous natural and explosive triggered storm slab avalanches up to size 2 were reported at all aspects and elevations.

Snowpack Summary

20-35 cm of new snow and strong southwest winds have formed fresh storm slabs.

Around 50 to 90 cm deep lies a potential weak layer of faceted snow at higher elevations, and surface hoar at lower elevations.

A mid-November melt-freeze crust is buried 60 to 100 cm below the surface at lower-alpine elevations (around 2400 m) and below, but this crust appears to be absent in higher-alpine terrain.

Snowpack depths at treeline range from 90 to 140 cm and decrease rapidly at lower elevations.

Weather Summary

Wednesday Night
Mostly clear skies. 40 km/h west ridgetop wind. Treeline temperature -8 °C. Freezing level valley bottom.

Thursday
Mostly cloudy with flurries. 3 to 10 cm of snow. 35 km/h southwest ridgetop wind. Treeline temperature -8 °C. Freezing level 1100 m.

Friday
Mostly cloudy. 30 km/h west ridgetop wind. Treeline temperature -5 °C. Freezing level 1600 m, dropping to valley bottom.

Saturday
Mostly cloudy with isolated flurries. 0-5 cm of snow. 35 km/h southwest ridgetop wind. Treeline temperature -7 °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.
  • Avoid freshly wind-loaded features, especially near ridge crests, rollovers, and in steep terrain.
  • Use small, low consequence slopes to test the bond of the new snow.
  • Be aware of the potential for large avalanches due to buried weak layers.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.