Avalanche Forecast

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Wednesday night: Decreasing cloud, moderate west wind, alpine temperature -16 C.

Thursday: Increasing cloud, isolated flurries with trace accumulations, light west wind, alpine high temperature -11 C.

Friday: Cloudy, 5-15 cm of snow, moderate south wind, alpine high temperature -10 C.

Saturday: Cloudy, 5-10 cm of snow, light south wind, alpine high temperature -9 C. 

A widespread avalanche cycle occurred overnight and into Wednesday. Numerous large (size 2-2.5) and very large (size 3-3.5) avalanches released from natural, human, and explosive triggers in the storm snow. The majority of the human-triggered avalanche activity occurred where the wind played a role in stiffening slabs, particularly below ridge crests.

Prior to the storm, there were many reports of large (size 2-3) avalanches from both natural and human triggers on a variety of aspects and elevations. These avalanches were breaking 50-100 cm deep on surface hoar layers from mid to late December. Several of them were remote-triggered. The most recent example, reported Monday, released naturally with loading from new snow and wind. These avalanches give clear evidence that the continual loading on this fundamentally weak snowpack structure remains a concern.

Within the past week, three notable deep persistent slab avalanches released naturally on east and northeast facing slopes above 2200 m in the southern part of the region on a crust/facet layer from late November buried 150 cm deep. 

The most recent storm delivered 30-70 cm of new snow across the region with moderate to strong southwest winds. Expect storm slabs to be especially touchy in lee terrain features where southwest winds have been drifting new snow into stiffer, more reactive slabs. Periods of sun possible on Wednesday have the potential to promote instability in the storm snow on sun-affected slopes.  

Two layers of surface hoar from mid and late December are now buried 60-140 cm deep. These layers continue to produce large avalanches across aspects and elevations. Small avalanches in the new snow have the potential to step-down to these persistent weak layers.

A facet/crust layer from late November lingers near the bottom of the snowpack. This layer has shown reactivity in isolated areas in the southern part of the region.

• Continue to make conservative terrain choices while the storm snow settles and stabilizes.
• Keep in mind that human triggering potential persists as natural avalanching tapers off.
• If triggered, storm slabs in-motion may step down to deeper layers and result in very large avalanches.