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Avalanche Forecast

Archived

Mar 11th, 2020–Mar 12th, 2020

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 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.

Regions

Lizard-Flathead.

Use caution as you transition into wind exposed terrain, new snow combined with strong winds have promoted wind slab development at upper elevations.

Confidence

Moderate -

Weather Forecast

WEDNESDAY NIGHT- Clear with cloudy periods / northwest wind, 20-30 km/h / alpine low temperature near -11

THURSDAY- A mix of sun and cloud / northwest wind, 20-30 km/h / alpine high temperature near -10

FRIDAY- Mainly cloudy with flurries, 5-10 cm / northeast wind, 20-40 km/h / alpine high temperature near -12

SATURDAY- Mainly cloudy with flurries, 5 cm / northeast wind, 30-50 km/h / alpine high temperature near -22

Avalanche Summary

Wind slabs at upper elevations may be reactive to human triggers. Cornices have also grown large with the recent weather pattern, and a cornice failure could trigger a wind slab avalanche on the slope below.

On Tuesday, there were a few reports of cornice triggered wind slab avalanches up to size 1.5.

On Monday, there were several natural, human and explosives triggered storm slab avalanches up to size 2. These were mostly on north through east aspects around 2000 m.

On Sunday, loose dry and soft slab avalanches were sensitive to human triggering and explosives avalanche control work to size 1.5. Avalanches have been 10 to 20 cm in depth, running fast and far. 

Snowpack Summary

10-15 cm of fresh snow from Tuesday night with ongoing strong winds will continue to promote wind slab development.

A total of 30 to 50 cm of recent storm snow sits on buried wind slabs in exposed areas and a sun crust on solar aspects (south through west facing slopes). Melt-freeze crusts extend up to 1900 m on other aspects. 

A thick crust that has facets associated with it sits 30-60 cm below the surface. There has been only one avalanche reported on this layer since February 17th. The middle of the snowpack is generally strong, but the base of the snowpack contains weak basal facets that are most prominent in shallow rocky start zones.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Avoid exposure to slopes that have cornices overhead.

Problems

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.