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Avalanche Forecast

Archived

Dec 25th, 2019–Dec 26th, 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

South Rockies.

Snow continues to settle over a deep persistent weak layer, which very recently produced very large avalanches. Any additional load, such as a smaller avalanche, cornice failure, or person, could trigger large and destructive avalanches.

Confidence

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

Weather Forecast

Wednesday Night: Cloudy with starry breaks. Alpine temperature -9 C. West wind, 10-15 km/hr.

Thursday: Mix of sun and cloud. Alpine temperature -9 C. West wind, 15-35 km/hr.

Friday: Mainly cloudy. Alpine temperature -12 C. West wind 15-35 km/hr.

Saturday: Sunny with cloudy breaks. Alpine temperature, -8 C. West wind, 10-20 km/hr.

Avalanche Summary

A natural avalanche cycle occurred Saturday with heavy loading from snow/rain. The intense loading triggered large (size 2) storm slab avalanches and very large (2.5-3) deep persistent avalanches.

On Saturday and into Sunday, large storm slab, wet slab and deep persistent avalanches were reported. Explosives triggered storm slab avalanches to size 2 in upper elevations and skiers triggered wet slab avalanches to size 2 at lower elevations. Most notable (and concerning) were reports of both natural and explosives triggering very large (up to size 3) deep persistent slab avalanches with avalanche crowns 40-200 cm.

Most recently on Wednesday, wind slabs to size 2 were reactive to explosives.

Snowpack Summary

Upwards of 50-100 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 1600 m, rain saturated the snowpack.

The bottom 30-50 cm of the snowpack consists of weak facets and crusts from November and October, these weak layers are the failure plane for recent large (size 2-2.5) deep persistant avalanches. The latest forecaster blog discusses managing this complex avalanche problem, check it out here.

Snowpack depths range between 80-200 cm around treeline and taper rapidly below.

Terrain and Travel

  • Minimize exposure to overhead avalanche terrain, large avalanches may reach the end of runout zones.
  • Be aware of the potential for large avalanches due to the presence of a deep persistent slab.
  • Cornice failure may trigger large avalanches.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.