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Avalanche Forecast

Archived

Feb 20th, 2025–Feb 21st, 2025

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

Regions

Lizard-Flathead, Flathead, Lizard.

The wind is forecast to pick up and the temperature continues to rise. Watch for persistent slabs to become more reactive.

Confidence

Moderate

Avalanche Summary

There have been numerous, small to large (size 1 to 2) dry and wet loose avalanches, both natural- and rider-triggered running in steep terrain over the past few days.

On Tuesday there were two reports of size 1.5 skier and snowmobile triggered persistent slab avalanches on a southeast and northwest aspects in the alpine. See details in this MIN here as well as this MIN here.

Snowpack Summary

20 to 30 cm of recent snow is sitting on 30 to 60 cm of faceted old snow. Below this is a persistent weak layer consisting of facets and surface hoar buried in late January.

The mid and lower snowpack is generally well settled, with no other layers of concern.

Weather Summary

Thursday Night

Cloudy with 0 to 1 cm of snow. 20 to 40 km/h southwest ridgetop wind. Treeline temperature -6 °C.

Friday

Mainly cloudy. 30 to 50 km/h southwest ridgetop wind. Treeline temperature -4 °C.

Saturday

Mostly cloudy with 5-10 cm of snow. 30 to 60 km/h southwest ridgetop wind. Treeline temperature -1 °C.

Sunday

Mostly cloudy with 15 to 25 cm of snow. 30 to 60 km/h southwest ridgetop wind. Treeline temperature 0 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.
  • Pay attention to the wind; once it starts to blow, sensitive wind slabs are likely to form.
  • Loose avalanches may step down to deeper layers, resulting in larger avalanches.
  • Make observations and continually assess conditions as you travel.

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.

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.