Avalanche Forecast

Wednesday night: Cloudy, isolated flurries with 1-3 cm of snow, moderate northwest winds, alpine temperatures near -6 C with freezing levels dropping below 500 m.

Thursday: Cloudy, 5-10 cm of snow, moderate southwest winds, alpine high temperatures near -6 C.

Friday: Cloudy, above 1600 m 80-100 cm of snow possible overnight and throughout the day with heavy rain below, strong south winds, alpine high temperatures near 0 C with freezing levels rapidly rising to 1600 m.

Saturday: Cloudy, another 40-60 cm of snow possible overnight and during the day with freezing levels dropping to 800 m, moderate southwest winds, alpine high temperatures around -3 C.  

Numerous large (size 2-2.5) natural, human-triggered, and explosive-triggered avalanches were reported Wednesday across aspects and elevations. Many of these avalanches failed at the storm interface and a few stepped down to the deeper November crust persistent weak layer. A couple of these avalanches were triggered by cornice fall.

The possibility for large human-triggered slab avalanches remains a serious concern for Thursday at higher elevations, especially as sensitive storm slabs create the potential for avalanches to step-down to these layers.

The recent storm added a significant new load to our snowpack, creating a widespread storm slab problem. This problem is likely to be more pronounced at higher elevations where southwest winds have exacerbated the reactivity of the new snow in drifted areas. The new snow is falling on another recent layer of surface hoar that has been showing increasing reactivity as snow accumulates.

Buried deeper in the snowpack, there are multiple weak layers, which include a variable layer of surface hoar and crust from mid-December (down 70-90 cm) as well as a deeper layer of sugary facets and crust buried in late-November (down 120-200 cm). Both of these persistent weak layers produced many large and destructive avalanches during and in the days after the storm December 19-21. Snowpack tests continue to produce sudden and propagating results on these layers (like this MIN report from Disease Ridge on Sunday). This fundamentally unstable snowpack structure remains a serious concern as new snow and wind add a critical load and increase the likelihood of triggering large and destructive avalanches.

• Continue to make conservative terrain choices while the storm snow settles and stabilizes.
• If triggered, storm slabs in-motion may step down to deeper layers and result in very large avalanches.