Avalanche Forecast

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

Monday night: Mostly clear, light variable winds, alpine temperatures near -14 C.

Tuesday: Increasing cloud, scattered flurries moving in overnight with up to 5 cm of accumulation, winds shift to the southwest and increase to strong, alpine high temperatures around -7 C.

Wednesday: Mix of sun and cloud, light west winds, alpine high temperatures near -11 C.

Thursday: Mainly sunny, light variable winds, alpine high temperatures near -13 C. 

Strong winds on Tuesday are expected to continue to build wind slabs that may be possible to human trigger in leeward features. Over the past 48 hours, operators in neighboring Glacier National Park have reported numerous large (size 2-2.5) wind slabs releasing naturally in the recent snow. Cornices may be reaching their breaking point and can act as triggers on slopes below.  

 50-70 cm of snow from the past week has buried a Jan 11th weak of layer of surface hoar. This persistent weak layer is most suspect in sheltered, open slopes at treeline. A lack of signs of instability from this layer suggest that the likelihood of triggering is decreasing. 

An extensive natural avalanche cycle occurred during last week's storm as up to 70 cm of new snow blanketed the region and was subsequently redistributed by strong winds. Several of these avalanches were thought to have stepped down to deeper layers (see this MIN report from Mt. MacPherson for an example). Avalanches breaking in the recent storm snow have the potential to step down to deeper layers, creating larger and more destructive avalanches.

 Recent snow accumulations ranging from 10-25 cm are being redistributed by variable winds. Winds switched direction from the southwest to the northwest, creating a tricky wind-loading pattern at upper elevations. Winds are forecast to shift back to the southwest and to increase on Tuesday, keeping wind slabs on lee features as a primary concern. 

50-70 cm of snow from the past week has buried a weak of layer of surface hoar that is likely to be preserved in sheltered, open slopes at and below treeline. Snowpacks tests on this layer show increasingly resistant results. 

A couple of older persistent weak layers exist in the mid to lower snowpack. The distribution of these layers is variable, but they follow a similar pattern to the layer discussed above. The upper layer from late December, down about 70-120 cm, consists of spotty surface hoar at shaded treeline and below treeline elevations. The lower layer from early December buried 120-190 cm deep consists of a combination of decomposing surface hoar with a crust and faceted snow. These lower layers are now largely unreactive.

• Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
• Be aware of highly variable recent wind loading patterns.
• If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.