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Avalanche Forecast

Archived

Mar 19th, 2025–Mar 20th, 2025

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

Regions

Lizard-Flathead, Flathead, Lizard.

Conditions are expected to remain primed for human-triggered avalanches. Triggering is most likely at treeline and above on wind-loaded slopes.

Confidence

Moderate

Avalanche Summary

On Tuesday, several natural cornice releases were observed. Only one of these triggered a small slab on the slope below. Explosives triggered a variety of storm slabs, wind slabs, cornices, and one persistent slab.

On Monday, numerous naturally triggered (by either wind or cornice fall) storm slab avalanches up to size 2.5 were reported on primarily northerly aspects in the alpine.

Snowpack Summary

Up to 60 cm of recent snow and southwest winds formed slabs reactive to human triggers.

In most areas, the storm snow rests 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

Wednesday Night

Mostly cloudy with a chance of light flurries. 20 to 40 km/h southwest ridgetop winds. Treeline temperature -5 °C. Freezing level near valley bottom.

Thursday

Cloudy with snowfall 5-15 cm. 20 to 40 km/h southwest ridgetop winds. Treeline temperature -3 °C. Freezing level 1500 m.

Friday

Cloudy with snowfall 10-20 cm. 30 to 50 km/h southwest ridgetop winds. Treeline temperature -2 °C. Freezing level 1700 m.

Saturday

A mix of sun and cloud. 15 to 30 km/h west ridgetop winds. Treeline temperature -3 °C. Freezing level 1600 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Avoid steep, rocky, and wind-affected areas where triggering slabs is more likely.

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.