South Columbia

Lingering wind slabs may still be reactive to human triggers in steep exposed terrain.

Moderate - Wind effect is extremely variable

THURSDAY: A mix of sun and cloud, light southwesterly winds, and freezing levels in valley bottoms with alpine temperatures reaching -10 C.FRIDAY: A mix of sun and cloud, light southwesterly winds, and freezing levels in valley bottoms with alpine temperatures reaching -5 C.SATURDAY: A mix of sun and cloud, light southwesterly winds, and freezing levels rising as high as 2200 m.

On Tuesday, avalanche activity generally tapered-off; however, there was one report of a cornice failure triggering a Size 2 slab avalanche failing within the recent storm snow. On Monday, explosives control triggered a couple of size 1-1.5 slab avalanches at treeline and in the alpine in the southeast corner of the region. These isolated slab avalanches, which failed on a recently buried facet / surface hoar interface, were up to 40cm deep at the crown and ran up to 150mLingering wind slabs are expected to be an isolated concern. These should be expected in steep and unsupported or convex wind loaded terrain features. In some areas, recently buried facets and surface hoar may prolong the reactivity of near-surface slab avalanches.

20-50 cm of recent snow typically overlies the variable mid-January interface with the largest amounts in the north of the region. The buried interface consists of old wind affected surfaces in exposed terrain, surface hoar in sheltered areas, widespread faceted old snow, and/or a sun crust on steep solar aspects. The bond between the new snow and the old surface has generally gained a lot of strength with the colder temperatures that followed the storm but weaknesses may still be lingering, especially where surface hoar is preserved. Strong southwest winds during the storm had redistributed the new snow and developed wind slabs in leeward terrain features. Isolated moderate outflow winds may have more recently resulted in reverse wind loading.The mid-December facet/surface hoar persistent weak layer can be found buried 70-120 cm deep and is generally considered dormant. However, we are still receiving occasional reports of sudden results in snowpack tests, suggesting that it has to potential to propagate into a large avalanche if triggered. This layer remains a concern for shallow snowpack areas where the layer is closer to the snow surface.