South Columbia

The trees are NOT a safe haven right now as a persistent weak layer at lower elevations remains sensitive to human triggers. Snow and wind from the weekend storm will likely form touchy storm slabs in wind exposed terrain at upper elevations too.

Low - Timing, track, or intensity of incoming weather system is uncertain on Sunday

A tightly wound and rapidly deepening low pressure center is expected to track just south of Vancouver Island Saturday afternoon. The northern edge of this system should track through the Columbias Saturday night with lingering convection generating continued snowfall through the day Sunday. A ridge is expected to take over the pattern Monday afternoon and should persist through Wednesday. SATURDAY NIGHT: 5 to 20cm of snow, freezing level at 500m, moderate to strong SW winds. SUNDAY: 2 to 10cm of snow, freezing level rising to 1000m, moderate to strong SW winds. MONDAY: Trace of snow, freezing level near valley bottom, light NW winds. TUESDAY: No snow expected, freezing level at valley bottom, light variable winds.

On Friday avalanche observations were limited to small cornice fall avalanches triggered by control work. Recent observations have been very limited, but I suspect that avalanche activity has been more widespread than the current data set would lead us to believe. On Thursday a very large natural avalanche was observed on a SE facing feature at 2000m that initially failed below ridge crest and ran full path. In the neighboring North Columbia's Thursday was a very active day with the following activity being reported: "A large natural avalanche cycle occurred on Thursday with several large natural avalanches to size 3 being reported on all aspects between 1300 and 2400m. A few smaller rider triggered avalanches were also reported in various drainages on NE facing slopes. One of the most interesting observations was of numerous avalanches to size 2.5 running on all aspects between 1400 and 1600m north of Revelstoke. These were likely running on the early December surface hoar."

A string of storms between December 2nd and December 11th produced 70 - 110cm of storm snow in the South Columbias which is settling settling out at all elevations. You may find a brittle crust about 10 to 30cm below the snow surface as high as 2000m that was formed by rain and warm temperatures last Tuesday. Below all the new snow lies the early December persistent weak layer. This weak layer manifests as an old sun crust on due south facing features in the alpine, large grained surface hoar below 1800m and small facets in isolated pockets. The surface hoar is the major player and it's been most reactive below treeline between 1400 and 1800m. Recent winds out of the south and southwest have formed wind slabs on lee features that are mainly confined to the alpine, but you may find the odd fresh wind slab at treeline too. The mid and lower portions of the snowpack are thought to be well settled.