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Avalanche Forecast

Archived

Jan 6th, 2020–Jan 7th, 2020

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

There is uncertainty with snowfall amounts Monday night through Tuesday. Avalanche danger is expected to rise as snow accumulates through the day on Tuesday.

Confidence

Moderate - Forecast precipitation (either snow or rain) amounts are uncertain.

Weather Forecast

Monday Night: Snow, accumulation 10-20 cm. Light to moderate west winds. Alpine temperatures around -5 C. Freezing level 700 m

Tuesday: Snow, accumulation 20-30 cm with another 15-25 cm through Tuesday night. Moderate southwest winds. Alpine temperatures around -3 C. Freezing level 1300 m.

Wednesday: Scattered flurries, accumulation 5-10 cm. Moderate southwest winds. Alpine temperatures around -3 C, freezing level 1200 m.

Thursday: Mainly cloudy. Light northwest winds. Alpine temperatures around -10 C. Freezing level valley bottom.

Avalanche Summary

Expect to see an increase in storm slab activity as the wind picks up and new snow accumulates on Tuesday.

This MIN from Harvey on Saturday includes a photo of a size 1 wind slab avalanche in the lee of a ridge feature below treeline, and describes signs of instability like shooting cracks.

Snowpack Summary

20-30 cm of new snow has now obscured widespread wind affected snow that extended well below tree line. Recent Cornice growth in the alpine has been notable.

Several crusts layers have formed in the mid to upper snowpack as a result of recent warming and rain events. As these crusts become buried deeper, they have the potential to turn into a persistent slab problem. We'll be keeping an eye on them going forward.

The lower snowpack consists of weak faceted snow and decomposing crusts but has not been an active avalanche problem recently.

Terrain and Travel

  • Watch for fresh storm slabs building throughout the day.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Keep your guard up at lower elevations. Wind slab formation has been extensive.

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.