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Avalanche Forecast

Archived

Dec 23rd, 2019–Dec 24th, 2019

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

Regions

Lizard-Flathead.

A huge amount of snow and rain has stressed and overloaded a weak crust deep in the snowpack. 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

Monday Night: Mostly cloudy with isolated flurries, trace to 10 cm. Alpine temperature -7 C. Southwest wind, 15-25 km/hr. Freezing level 1100 m.

Tuesday: Mainly cloudy. Alpine temperature -7 C. Southwest wind, 20-30 km/hr. Freezing level at valley bottom.

Wednesday: Mix of sun and cloud. Alpine temperature -9 C. West wind, 10-20 km/hr.

Thursday: Mix of sun and cloud. Alpine temperature -6 C, possible inversion. West wind, 15-30 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. A complex avalanche problem has developed, read the latest forecaster blog here.

Snowpack Summary

Upwards of 70 cm storm snow is settling around the region. At higher elevations into the alpine, wind is impacting loose, dry snow, and building wind slabs and cornices. Up to 1650 m, rain saturated the snowpack and a crust can be found under 10-20 cm low density snow. Below 1400 m, an isothermal snowpack is expected to recover with cold temperatures.

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.

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

Terrain and Travel

  • Storm slabs in motion may step down to deeply buried weak layers resulting in very large avalanches.
  • Cornice failure may trigger large avalanches.
  • Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.