Avalanche Forecast

Archived

Dec 8th, 2022–Dec 9th, 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, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Lizard-Flathead, Akamina, Flathead, Lizard.

Updated 8 am: Overnight snowfall and wind are forming fresh storm slabs and adding load to a buried weak layer.

Keep your terrain choices conservative and assess conditions while you travel. Watch and feel for signs of instability such as whumpfing, cracking, and new avalanches.

Confidence

Moderate

Avalanche Summary

No new natural avalanches observed since the weekend. Avalanches triggered with explosives, that were focused on wind slabs, were reported by local operators. These were small size one avalanches.

This past 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 reactive. Loose-dry avalanches (sluffing) of the surface snow from steep slopes and terrain features should also be expected.

Snowpack Summary

In less than a week, about 40 cm of low-density snow has fallen. Southwesterly winds have redistributed much of this 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

Thursday Night

Mainly cloud, 5 cm accumulation, winds southwest 20 gusting to 45 km/h, temperature -6 C at 1500 m.

Friday

Cloudy with possible sunny periods, 2 cm accumulation, winds southwest 15 gusting to 35 km/h, temperature -4 C at 1500 m.

Saturday

Mainly cloudy, trace accumulation, winds south 10 km/h, temperature -5 C at 1500m.

Sunday

Cloudy with sunny periods, 3 cm accumulation, winds south 10 km/h, temperature -3 C at 1500 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.
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.
The likelihood of deep persistent slab avalanches will increase with each day of warm weather.

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.