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Avalanche Forecast

Archived

Dec 5th, 2022–Dec 6th, 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 unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
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.

Conditions are more complicated than what meets the eye. Fresh, reactive wind slabs are expected to form at upper elevations. Riders may be drawn to more sheltered areas around treeline to avoid these wind slabs, but should consider that this is where the persistent slab problem has been most problematic to date. Keep your terrain choices conservative and don't let good riding lure you into steeper terrain.

Confidence

Moderate

Avalanche Summary

On Sunday, a MIN report from Tunnel Creek reported reactivity in a snowpack test on the Mid-November layer on a south aspect. In this area, the layer presented as facets on a crust. They also observed a large natural avalanche on a west-facing slope at treeline. (Thanks for the report- ESPETERS10)

On Saturday, a small (size 1.5) skier triggered persistent slab avalanche occurred on an east-facing slope at treeline.

Numerous reports of small loose dry avalanches (sluffing) have been reported within the recently fallen low-density surface snow.

We have very few eyes out there. If you do get out please consider reporting in the MIN.

Snowpack Summary

Overnight and throughout the day 5-15 cm of new snow is expected. 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 into fresh wind slabs. In sheltered terrain, cold temperatures will likely maintain low-density, powdery snow.

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

Monday night

Cloudy with snowfall, 5-10 cm of accumulation expected. Westerly winds 20-35 km/h at ridgetop. Treeline temperatures drop to -13 C.

Tuesday

Cloudy with snowfall, generally ~5 cm accumulation, up to 15 cm in the far south of the region. Westerly winds 25-40 km/h at ridgetop. Treeline temperatures reach a high of -10 C.

Wednesday

Cloudy with light snowfall, up to 4 cm of accumulation. Westerly winds 15-30 km/h at ridgetop. Treeline temperatures reach a high of -8 C.

Thursday

More of the same! Cloudy with snowfall, up to 5 cm of accumulation. Westerly winds 25-45 km/h at ridgetop. Treeline temperatures reach a high of -6 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.
  • Wind slabs are most reactive during their formation.
  • 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.