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Avalanche Forecast

Archived

Dec 7th, 2022–Dec 8th, 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 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.

Regions

Lizard-Flathead, Akamina, Flathead, Lizard.

Reactive wind slabs may exist at upper elevations. Watch and feel for signs of instability such as whumpfing, cracking, and new avalanches. If you seek more sheltered areas at treeline you should consider that this is where the persistent slab has been most reactive in snowpack tests. Keep your terrain choices conservative and assess conditions while you travel.

Confidence

Moderate

Avalanche Summary

On Tuesday no natural avalanches were reported, however, a few skier-controlled and explosive controlled wind slabs up to size 1 were seen.

Last Sunday, a MIN report from Tunnel Creek reported reactivity in a snowpack test on the Mid-November layer on a south aspect. They also observed a large natural avalanche on a west-facing slope at treeline.

With continued moderate to strong winds and slightly warmer temperatures, wind slabs may be present and reactive on Thursday as well as loose dry avalanches (sluffing) of the surface snow from steep slopes and terrain features.

Snowpack Summary

Up to 20 cm of low-density snow fell by Wednesday morning. This new snow will add to the ~25 cm of storm snow that fell early in the weekend. In wind-affected terrain, westerly winds are expected to redistribute this new snow building fresh wind slabs. In sheltered terrain, slightly warmer temperatures may start to consolidate the recent snow into more of a slab.

The middle of the snowpack consists of weak sugary layers of facets and surface hoar. A widespread rain crust remains near the ground at treeline and below treeline.

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

Weather Summary

Wednesday Night

Unsettled weather overnight bringing up to 5 cm of new snow. Westerly winds 15-25 km/h at ridgetop. Temperatures near -9 C and freezing levels valley bottom.

Thursday

Cloudy with isolated flurries. Moderate to strong southwesterly winds at ridgetop. Temperatures reach a high of -4 C.

Friday

New snow 5-10 cm. Southwest wind 20-40 km/h with stronger gusts. Average temperature near -8 C.

Saturday

A mix of sun and cloud. Flurries. Winds generally light from the southwest. Treeline temperatures reach a high of -5 C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Expect slab conditions to change drastically as you move into wind exposed terrain.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.

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.