South Columbia

Strong winds have made triggering wind slab avalanches possible at upper elevations. Be careful in drifted areas and assess open slopes and rollovers where a weak layer may be preserved. 

Tuesday night: Mostly cloudy, scattered flurries with up to 5 cm of accumulation, moderate west winds, alpine temperatures around -10 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 -12 C.

Friday: Mainly sunny, light north winds, alpine high temperatures near -13 C. 

Recent strong west winds are expected to have formed wind slabs in lee features at upper elevations that may be possible to human trigger. Over the last few days, operators in neighboring Glacier National Park reported several large (size 2-2.5) wind slabs releasing naturally on a variety of aspects. Cornices may be reaching their breaking point and can act as triggers on slopes below. 

On Monday, several operators in the region reported small (size 1-1.5) human-triggered avalanches releasing on a weak layer of surface hoar on north, east and southeast aspects at treeline and below treeline elevations. These avalanches were breaking 25-45 cm deep.

Winds have varied in speed and direction from southwest to northwest over the past few days and have redistributed the 10-25 cm of snow that fell over the weekend into a tricky loading pattern. Ongoing snow and wind over the past week have contributed to notable cornice growth. 

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. Observers in the south of the region continue to report sudden results in the snowpack tests and shooting cracks on this layer. Don't let decreasing winds and a clearing trend on Wednesday lure you into committing terrain. Recent avalanche activity demonstrates that this layer is likely to be reactive where it is preserved and that it warrants careful assessment. 

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. Snowpack tests on these layers show increasingly unreactive results, suggesting a trend towards dormancy. 

• Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
• Be aware of highly variable recent wind loading patterns.
• Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
• If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.