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Avalanche Forecast

Archived

Jan 16th, 2020–Jan 17th, 2020

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.

A stealthy inversion has recently slipped into the alpine, hastening the snowpack's transition out of the deep freeze. If there's one thing the snowpack hates, it's rapid change. Remember those basal facets? Be wary if they start to wake up...

Confidence

Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

Thursday night: Mostly cloudy with flurries bringing 5-10 cm of new snow. Light to moderate west winds. Alpine temperatures around -12. 

Friday: Mix of sun and cloud. Light to moderate southwest winds, strong at ridgetop. Alpine high around -12.

Saturday: Mix of sun and cloud with isolated flurries bringing a trace of new snow. Light to moderate southwest winds, strong at ridgetop. Alpine high around -8.

Sunday: Mix of sun and cloud. Moderate southwest winds, strong at ridgetop. Alpine high around -3.

Avalanche Summary

Avalanche reports from Thursday were predominantly skier triggered windslabs up to size 1.5. Our field team also reported a natural size 2 windslab avalanche that stepped down to the deep persistent basal facets below a rock band. This is the type of terrain where the deep persistent basal facets will typically be triggered. In the coming days, the warming period may provoke a resurgence in persistent slab avalanche activity.

Snowpack Summary

Recent snow has been loaded into pockets of soft windslab in alpine lees, and is settling in the mild alpine temperatures. At lower, colder, calmer elevations it may remain unconsolidated. It sits over widespread windslab in exposed areas at all elevations.

A well consolidated mid-snowpack overlies a generally weak basal snowpack. The bottom 10-20 cm of the snowpack consists of facets and deteriorating crusts. This basal layer has gradually been gaining strength, but potential still exists for large triggers in thin, rocky areas to trigger avalanches at this depth.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Seek out wind sheltered terrain below treeline where you can avoid wind slabs and find great riding.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Avoid rock outcroppings, convexities, and anywhere the snowpack is thin and/or variable.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.