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Avalanche Forecast

Archived

Dec 19th, 2024–Dec 20th, 2024

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

Regions

Lizard-Flathead, Flathead, Lizard.

Recent storm snow is still settling and needs time to bond. Carefully assess the upper snowpack for instabilities before entering any steeper terrain.

Confidence

Moderate

Avalanche Summary

A widespread avalanche cycle took place on Wednesday, with numerous natural, skier, and explosive-triggered avalanches reported across various elevations and aspects, up to size 2. These slab avalanches primarily failed in the upper 40 cm of recent storm snow.

One report of a skier-triggered, size 1 avalanche, below treeline in the Lizard range suggests that buried surface hoar may remain reactive in steep terrain at lower elevations.

Snowpack Summary

Recent snowfall has brought up to 40 cm of snow, with deeper deposits accumulating in lee-facing terrain at higher elevations due to southwest winds.

The mid and lower snowpack is generally well-settled and stable. However, there is some uncertainty about a potential surface hoar layer buried 50 to 80 cm deep, which could be reactive on isolated, steep, sheltered slopes around treeline and below.

Snow depths at treeline range from 120 to 180 cm.

Weather Summary

Thursday Night

Cloud building overnight with 0 to 2 cm of snow. 30 to 50 km/h southwest ridgetop wind. Treeline temperature -3 °C.

Friday

Mostly cloudy. 20 to 40 km/h southwest ridgetop wind. Treeline temperature -2 °C. Freezing level rising to 2000 m.

Saturday

Mix of sun and cloud. 10 to 30 km/h south ridgetop wind. Treeline temperature +1 °C. Freezing level 2400 m.

Sunday

Mix of sun and cloud. 20 to 40 southwest ridgetop wind. Treeline temperature -4 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Avoid freshly wind-loaded terrain features.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Approach steep and open slopes at and below treeline cautiously, as buried surface hoar may exist.

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.