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Avalanche Forecast

Archived

Dec 12th, 2022–Dec 13th, 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.

Large skier-triggered avalanches occurred this past weekend!

A buried weak layer and developing wind slab will make backcountry travel challenging. Watch out for signs of instability such as whumpfs and shooting cracks and terrain features such as convex rolls and cross-loaded features. Check out our latest blog for how to manage this problem.

Watch out for signs of instability such as whumpfs and shooting cracks and terrain features such as convex rolls and cross-loaded features.

Confidence

Moderate

Avalanche Summary

Avalanche activity has ramped up in the last few days. The most notable report came from a group of skiers who were involved in an avalanche in the Lizard Range. One person was buried but their companions were able to dig them out safely. This avalanche occurred on the mid-November weak layer.

The MIN has similar reports of this layer being triggered and creating large avalanches such as this one from Hosmer. Buried weak layers are difficult to predict and make travel through avalanche terrain a challenge. It seems that we have reached a tipping point and avalanche activity on this layer can be expected to continue.

A huge thank you to those who have supported the community and reported in the MIN.

Snowpack Summary

Since Thursday night up to 30 cm of snow has fallen. This is expected to be redistributed by west-northwest winds that have picked up since Sunday night. New wind slabs are expected to form on a variety of surfaces. In the alpine and at treeline on the northeast aspects, it sits mostly on older wind slabs. In more sheltered areas the newer lighter snow sits on about 20 to 30 cm of more consolidated snow. Just below this is where our mid-November weak layer, consisting of facets and surface hoar. A widespread rain crust remains near the ground, at the treeline, and below the treeline.

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

Weather Summary

Monday Night

Clear with cloudy periods, no accumulation, winds north 8 km/h, temperature -13 C at 1500 m.

Tuesday

Sunny with cloudy periods, trace accumulation, winds northwest 10 km/h, temperature -9 C at 1500 m.

Wednesday

Cloudy with possible sunny periods, up to 3 cm accumulation, winds west 10 km/h, temperature -12 C at 1500 m.

Thursday

Cloudy with sunny periods, 2 cm accumulation, winds northeast 10 gusting to 25 km/h, temperature -12 C at 1500 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • If triggered, storm slabs in-motion may step down to deeper layers and result in very large avalanches.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.
  • Be especially cautious as you transition into wind affected terrain.

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.