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Avalanche Forecast

Archived

Dec 11th, 2022–Dec 12th, 2022

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

Regions

Lizard-Flathead, Akamina, Flathead, Lizard.

Large skier-triggered avalanches have occurred in our region in the last few days!

Storm slabs and buried weak layers can surprise and create large avalanches.

Assess conditions while you travel and choose your terrain carefully. Watch and feel for signs of instability such as whumpfing, cracking, and recent avalanches.

Confidence

Moderate

Avalanche Summary

A group of skiers reported triggering a large avalanche, size 2, that released on the mid-November weak layer. This layer is still around and can be expected to produce avalanches if triggered in the "right" spot or by a heavier load.

Late in the day Sunday there was a report of a large size 3, skier-triggered avalanche in the Lizard Range. Three people were involved, with one fully buried. They were dug out by their companions. Details are not yet known at this time but more information will follow.

Thank you all for supporting your community and reporting in the MIN.

Snowpack Summary

Up to 30 cm of snow has fallen since Thursday. This sits on a variety of surfaces. In the alpine and at treeline, it sits mostly on wind slabs that were created by southwesterly winds that we experienced earlier this past week.

Below the 30 cm of new snow sits 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

Sunday Night

Mostly cloudy, up to 5 cm accumulation, winds northeast 10 gusting to 30 km/h, temperature -10 C at 1500 m.

Monday

A mix of sun and cloud, trace accumulation, winds northeast 10 gusting to 30 km/h, temperature -10 C at 1500 m.

Tuesday

Cloud in the morning with more sun in the afternoon, no accumulation, winds northwest 10 to 20 km/h, temperature -9 C at 1500 m.

Wednesday

Cloudy with sunny periods, 2 cm accumulation, winds west 10 km/h, temperature -10 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.
  • 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.
  • Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.
  • If triggered, storm slabs in-motion may step down to deeper layers and result in very large avalanches.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.