Avalanche Forecast

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

Sunday night: Cloudy, 5-15 cm of snow, moderate west wind with strong gusts, alpine temperature -10 C, freezing level dropping from 1000 m to valley bottom.

Monday: Mostly cloudy with 5-10 cm of snow, light to moderate southwest wind, alpine high temperature -5 C.

Tuesday: Cloudy, 20-35 cm of snow overnight and throughout the day, moderate south wind, alpine high temperature -3 C, freezing level rising to 800 m in the afternoon.

Wednesday: Cloudy, 5-10 cm of snow, moderate west wind, alpine high temperature -3 C, freezing level dropping below 500 m.

Several human and explosive-triggered wind slabs were reported at treeline and alpine elevations on leeward aspects (northwest and northeast) on Saturday. These avalanches broke 10-40 cm deep and were small in size (size 1-1.5). Additional snowfall and wind transport overnight may increase the size of these slabs on Monday.

Observers also reported large (size 2-3) avalanches breaking on a layer of surface hoar from late or mid-December on a variety of aspects and elevations from natural, human, and explosive triggers over the weekend. A few of these avalanches were triggered remotely (i.e. from a distance). Three notable 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. These avalanches give clear evidence that the continual loading on this fundamentally weak snowpack structure remains a serious concern.

The most recent snow has been redistributed by strong southwest winds in exposed areas, loading lee features with stiffer, more reactive slabs.

There are multiple weak layers buried in the snowpack. A weak layer of feathery surface hoar is buried around 50 to 90 cm deep. Around 90 to 140 cm deep, another surface hoar layer may be found. Near the bottom of the snowpack, a facet/crust layer from late November is present. This fundamentally unstable snowpack structure remains a concern, as it is capable of producing large and destructive avalanches. It is possible that wind slab avalanches could step down to these deeper layers or the layers could be triggered in areas where the snowpack is relatively thin.

• Make conservative terrain choices and avoid overhead hazard.
• Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
• If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
• Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.