South Columbia

New snow and warming are influencing a complex snowpack: storm and wind slabs sit above three weak layers that are reactive at all elevations. Perform cautious route-finding without overhead exposure and avoid alpine terrain as the snowpack adjusts.

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

WEDNESDAY: Cloudy with light snowfall, accumulation 15-30 cm, light to moderate southerly winds, alpine temperature near -5 C, freezing level near 1300 m.THURSDAY: Cloudy with light snowfall, accumulation 5-10 cm, light to moderate southerly winds, alpine temperature near -9 C, freezing level near 700 m.FRIDAY: Partly cloudy, light southwesterly winds, alpine temperature near -10 C, freezing level below valley bottom.

On Monday, there were many reports of small to large (size 1 to 2) storm slabs triggered by skiers, generally on northerly and easterly aspects at all elevation bands, often releasing on the mid-January weak layer.  Below treeline, avalanches were releasing in open cutblocks.  There were also numerous reports of large (size 2 to 3) persistent slab avalanches, being triggered naturally and by skiers on northerly and easterly aspects, at treeline and alpine elevations, releasing on the early-January weak layer.  There was one report of a very large avalanche (size 3.5) releasing on either the mid-December weak layer or the November layer.Similar avalanches have been observed daily since last Wednesday.  Although we have been seeing general decreasing activity on the buried weak layers, expect to see more avalanches with the changing weather and where the weak layers are preserved, such as in sheltered locations in the alpine and treeline elevations and in open cutblocks and gullies below treeline.  Triggering such weak layers will likely produce large, destructive avalanches with high consequences.

The current snowpack is complex, we have three active weak layers that we are monitoring.60 to 90 cm of storm snow sits on a crust and/or surface hoar layer (mid-January). The crust is widespread, except possibly at high elevations on north aspects. The mid-January surface hoar is 5 to 20 mm in size and is likely present at all elevation bands. The recent storm snow fell with strong south winds, producing wind slabs in lee features at treeline and alpine elevations and in open areas below treeline.Deeper in the snowpack, a persistent weak layer known as the early-January layer is buried 70 to 110 cm. It is composed of surface hoar on sheltered slopes and a sun crust on steep solar aspects and is present at all elevation bands. Recent snowpack tests have shown sudden fracture characters with moderate loads and high propagation potential, as well as other signs of instability such as whumpfs and cracking. Yet another persistent weak layer buried mid-December is 100 to 150 cm deep and consists of a facet/surface hoar/crust combination. It is most problematic at and below tree line.A rain crust buried in November is 150 to 200 cm deep and is likely dormant for the time being.