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Avalanche Forecast

Archived

Jan 5th, 2022–Jan 6th, 2022

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

Regions

Lizard-Flathead.

As winds pick up ahead of the next storm, fresh, reactive wind slabs will likely form at upper elevations. The region continues to deal with a tricky persistent slab problem and very large avalanches remain possible. Conservative terrain selection remains essential.

Confidence

Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

Wednesday night: Increasing cloud. Light NW wind switching SW. Treeline temperature around -20 °C. 

Thursday: Snowfall starting 5-10 cm. Moderate SW wind. Treeline high around -12 °C. 

Friday: Snowfall 15-30 cm. Strong SW wind. Treeline high around -5 °C.

Saturday: Mostly cloudy. Moderate to strong SW wind. Treeline high around -8 °C.

Avalanche Summary

On Monday and Tuesday, storm slabs were reactive to explosive up to size 2 and ski cuts produced storm slabs and loose dry avalanches up to size 1. By Wednesday, explosive results were limited to size 1 loose dry.

On Sunday, a size 2.5 persistent slab avalanche was triggered on an E aspect at treeline. This MIN post goes into more details and has some great photos showing the nature of the problem and the type of terrain where this problem seems most prevalent. Last Friday, a size 2.5 persistent slab avalanche was reported on a north aspect at 2000 m elevation. This failed on the early December weak layer down 100-175 cm.  

Snowpack Summary

As winds pick up in advance of the next storm, 25-30 cm of recent snow will likely see redistribution into reactive slabs in lee terrain features. The recent snow sits over variable and potentially weak snow surfaces including widespread facets, wind affected snow, and/or surface hoar in sheltered areas.

The most notable layer of concern in the snowpack is a crust that was formed in early December and is now down 90-200 cm. Activity on this layer has been sporadic, but most recently produced large avalanches on January 2. This layer has created a low likelihood, high consequence scenario which is best managed through conservative terrain choices and disciplined backcountry travel techniques.

Terrain and Travel

  • Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
  • Seek out wind sheltered terrain below treeline where you can avoid wind slabs and find great riding.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.