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Avalanche Forecast

Archived

Dec 18th, 2025–Dec 19th, 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, human triggered possible.

Regions

Purcells, Crawford, East Purcell, St. Mary.

Storm slabs remain reactive to human triggers, especially in wind affected terrain.

Continue to make conservative terrain choices while the storm snow settles and stabilizes.

Confidence

Moderate

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

Avalanche Summary

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

20-35 cm of recent snow and strong southwest winds have formed fresh storm 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 140 cm down is a weak layer of faceted snow at higher elevations or surface hoar in sheltered terrain.

100 to 160 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

Thursday Night
Cloudy. 10 to 20 cm of snow. 30 km/h southwest ridgetop wind. Treeline temperature -5 °C. Freezing level 1600 m.

Friday
Mostly cloudy. 30 km/h west ridgetop wind. Treeline temperature -7 °C. Freezing level 1000 m.

Saturday
Mostly cloudy with isolated flurries. 0 to 5 cm of snow. 30 km/h southwest ridgetop wind. Treeline temperature -8 °C. Freezing level valley bottom.

Sunday
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.
  • 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.