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Avalanche Forecast

Archived

Dec 13th, 2022–Dec 14th, 2022

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, Akamina, Flathead, Lizard.

A buried weak layer has produced large rider-triggered avalanches in recent days. Keep your terrain choices conservative and be prepared to back off quickly if you find signs of instability like whumpfing, shooting cracks and recent avalanches.

Read our featured blog to learn more about how to manage a persistent slab problem when traveling in the backcountry.

Confidence

Moderate

Avalanche Summary

On Sunday, several large (size 2-3) persistent slab avalanches were reported. They were remotely triggered by skiers or snowmobiles at treeline elevations. Check out these MIN reports here and here. A huge thank you to the groups who shared their observations to the Mountain Information Network!

Since then, avalanche observations have been limited to small explosive-triggered wind slabs.

Snowpack Summary

A thin sun crust may be found on south aspects, while surface hoar grows at treeline and below. 30-50 cm of recent snow has been redistributed by previous winds at upper elevations. This recent snow may overlie surface hoar in wind sheltered areas.

A concerning weak layer consisting of facets and surface hoar formed in November is now buried 80-90 cm deep. At the bottom of the snowpack, a thick crust sits on the ground.

At treeline, snowpack depths vary from 120 to 200 cm.

Weather Summary

Tuesday night

Flurries bringing 3-8 cm. Light northeast wind. Alpine low -9 C.

Wednesday

Flurries in the morning bringing 4-8 cm then clearing. Light northeast wind. Alpine high -6 C.

Thursday

Mix of sun and cloud. Light northerly wind. Alpine high -9 C.

Friday

Mix of sun and cloud. Wind increasing to strong northwest. Alpine high -12 C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Be especially cautious as you transition into wind affected terrain.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Remote triggering is a concern, watch out for adjacent and overhead slopes.
  • The trees are not the safe-haven they normally are at this time. Terrain at treeline is primed for human triggered avalanches.

Problems

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.

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.