South Columbia

Storm conditions will create new problems for the weekend but don't forget about the tricky persistent slab problem. Large, destructive avalanches remain possible.

The snowfall is burying widespread 10-20mm surface hoar up, a sun crust on steep sun exposed slopes, and/or wind affected surfaces in the alpine. The problematic mid-December surface hoar/crust layer is typically down 80-120cm below the new snow and remains sensitive to human triggering is some areas. The reactivity of this persistent weak layer appears to be quite variable but still has the potential for large, destructive avalanches in some areas. The layer appears to be the most reactive at and below treeline.

Fair - Timing, track, or intensity of incoming weather system is uncertain

The cold front passes over the interior regions on Friday and should be finished by Friday evening. The South Columbia region can expect 10-15mm of precipitation with freezing levels of 1000-1200m. Alpine winds are expected to be strong from the SW but may switch to NW at the tail of the storm. On Saturday, light precipitation (1-3mm) is forecast with freezing levels around 800m and moderate SW alpine winds. The next frontal system is expected for Sunday and is forecast to bring another 10-15mm of precipitation.

On Wednesday, explosives triggered a cornice but the cornice did not trigger a slab.  On Tuesday, a natural size 2.5 persistent slab was reported.  This released on the mid-Dec weak layer.  Sluffing from steep sun exposed slopes was also reported. Some natural avalanche activity is expected on Friday in specific areas including fast sluffing from steep terrain and wind slabs in leeward alpine features. Small avalanches have the potential to step down and trigger a persistent slab which would greatly increase the consequences. Skier triggering is likely in wind loaded areas and steep terrain, and remains possible for persistent slabs where the tricky mid-December layer is still intact.