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Avalanche Forecast

Archived

Dec 24th, 2019–Dec 25th, 2019

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.
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.

A heavy load of recent snow is settling over a deep persistent weak layer. Any additional load, such as a smaller avalanche, cornice failure, or person, can result in large, destructive avalanches.

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

Tuesday Night: Mainly cloudy with isolated flurries. Alpine temperature -12 C. Southwest wind, 20-30 km/hr. Freezing level at valley bottom.

Wednesday: Mix of sun and cloud. Alpine temperature -9 C. West wind, 10-15 km/hr.

Thursday: Cloudy with isolated flurries. Alpine temperature -10 C, possible inversion. West wind, 15-25 km/hr.

Friday: Mainly cloudy and flurries, trace to 5 cm. Alpine temperature -12 C. Southwest wind 15-25 km/hr.

Avalanche Summary

Snow accumulation over the weekend overloaded deeply buried weak layers. A natural storm slab avalanche cycle to size 3 occurred Saturday and Sunday following intense and heavy loading from snow/rain and wind.

Explosives triggered very large (size 3-3.5) avalanches Saturday and Sunday, these avalanches failed on a deep persistent weak layer with some avalanche crowns over 2 m. On Monday explosives continued to produce large (size 2.5) avalanches, failing on the deep persistent weak layer. Explosives Tuesday continued to trigger large (size 2) deep persistent slab avalanches.

Snowpack Summary

The massive load of recent storm snow is settling around the region. Light winds will slowly redistribute loose snow. More recent flurries have left 10-30 cm lower density snow on the upper snowpack. Between 1400-1600 m, this loose snow overlies a rain crust. below 1400 m, a previously isothermal snowpack is recovering. 

Weak facets and decomposing crust layers from November and October can be found 80-140 cm below the surface. The intense loading of storm snow overloaded these weak layers, producing very large (size 3) avalanches on Saturday and Sunday triggered by explosives. A complex avalanche problem has developed, check out latest forecaster blog here.

Snowpack depths range between 60-160 cm at higher elevations and taper rapidly below treeline.

Terrain and Travel

  • Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.
  • Cornice failure may trigger large avalanches.
  • Be aware of the potential for large avalanches due to the presence of a deep persistent slab.