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Avalanche Forecast

Archived

Mar 13th, 2025–Mar 14th, 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, Bull.

Before entering avalanche terrain assess the bond of the new snow.

A persistent weak layer in the snow means avalanches could step down and become large.

Confidence

Moderate

Avalanche Summary

Wed/Thurs: Explosive control produced dry loose and storm slab avalanches to size 2 on north through east facing slopes. A natural size 2.5 storm slab was also observed.

Tues: A natural cycle of small (size 1 to 1.5) storm slab avalanches occurred.

Last weekend: Explosive control and natural cornice fall produced numerous slab avalanches up to size 2.

Looking forward: Storm slabs are expected to remain reactive and may step down to deeper persitstent weak layers.

Snowpack Summary

Recent snowfall of 20 to 40 cm combined with southwest winds has formed widespread and potentially reactive storm slabs. Below 1900 m and on sun-exposed slopes, the new snow rests atop a melt-freeze crust left by previous warm temperatures and sun. The snow surface may be moist or crusty at lower elevations.

A persistent weak layer of surface hoar or facets from late January is buried 90 to 150 cm. This layer triggered large avalanches earlier in March, and remains reactive in snowpack tests. The greatest concern for this weak layer lies in areas where a thick, supportive crust is absent under the new snow. The lower snowpack is generally well-settled and strong.

Weather Summary

Thursday Night

Mostly cloudy, with 1 to 5 cm of snow. 25 to 30 km/h southwest ridgetop wind. Treeline temperature -9 °C.

Friday

Partly cloudy, with trace amounts of snow possible. 20 to 30 km/h southwest ridgetop wind. Treeline temperature -7 °C.

Saturday

Cloudy, with 5 to 10 cm of new snow. 15 to 25 km/h south ridgetop wind. Treeline temperature -5 °C.

Sunday

Cloudy, with 1 to 5 cm of snow. 15 to 35 km/h southwest ridgetop wind. Treeline temperature -5 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Keep your guard up as storm slabs may remain sensitive to human triggering.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Be aware of the potential for large avalanches due to buried weak layers.
  • Be especially cautious as you transition into wind-affected terrain.

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.