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Avalanche Forecast

Archived

Mar 20th, 2025–Mar 21st, 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 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.

Regions

Lizard-Flathead, Flathead, Lizard.

Forecast snow and wind are expected to form fresh storm slabs reactive to human triggers.

Triggering will be most likely in wind affected terrain.

Confidence

Moderate

Avalanche Summary

On Wednesday, numerous explosive triggered storm slabs up to size 1.5 were reported primarily on northerly aspects at treeline and above.

Snowpack Summary

Forecast snow and wind are expected to form fresh storm slabs reactive to human triggers.

60 cm of recent snow sits on a melt-freeze crust, except for high-elevation north and east-facing slopes.

A persistent weak layer of surface hoar or facets from late January is buried 100 to 150 cm. Rocky slopes with a convex shape on northerly and easterly facing aspects at treeline and above are the most likely places to trigger this layer.

The lower snowpack is generally well-settled and strong.

Weather Summary

Thursday night

Cloudy with 3 to 10 cm of snow. 20 to 30 km/h southwest ridgetop winds. Treeline temperature -7 °C. Freezing level valley bottom.

Friday

Cloudy with 5 to 15 cm of snow. 30 to 40 km/h southwest ridgetop winds. Treeline temperature -3 °C. Freezing level 1700 m.

Saturday

Mix of sun and cloud with isolated flurries, 0 to 5 cm of snow. 10 to 20 km/h west winds. Treeline temperature -5 °C. Freezing level 1500 m.

Sunday

Mostly cloudy. 20 to 30 km/h southwest ridgetop winds. Treeline temperature -3 °C. Freezing level 1700 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks, or recent avalanches.
  • Use small, low consequence slopes to test the bond of the new snow.
  • Avoid steep, rocky, and wind-affected areas where triggering slabs is more likely.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.

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.