South Columbia

A new persistent weak layer has "woken-up" and warrants your attention. Read the whole bulletin for details.

Moderate - Wind effect is extremely variable

Wednesday: Overcast skies with light flurries / Moderate to strong southwest winds / Alpine temperature of -12Thursday: Overcast skies with light flurries / Moderate southerly winds / Alpine temperature of -7Friday: Overcast skies with light flurries / Light and variable winds / Alpine temperature of -10

In recent days, several natural storm slab avalanches to size 2 failed in response to new snow and wind. On Sunday in the southwest of the region a skier accidentally triggered a size 2 persistent slab avalanche which failed on the mid-February layer. The avalanche failed on a southwest facing slope below treeline and completely buried the skier who was successfully rescued by their party. On Monday in the southeast of the region another skier accidentally triggered a size 1.5 slab avalanche on the same layer. This avalanche also failed on a south aspect at 2000m with a buried crust acting as the failure plane.Another noteworthy occurrence was a naturally-triggered size 3 persistent slab avalanche which failed on the mid-January surface hoar. The avalanche, which is thought to have been triggered by sloughing from above, occurred in the Monashees near Revelstoke on a northeast facing slope at 1900m. Although this avalanche occurred north of Hwy 1 just outside the South Columbia region, it points to the continued reactivity of deeper persistent slabs in isolated terrain.

Since Saturday night, 25-50 cm of new snow fell. These accumulations cover old surfaces which include faceted powder, a sun crust on solar aspects and surface hoar on sheltered slopes. Strong winds will have redistributed much of the new snow into fresh wind slabs in exposed terrain. 50-80 cm below the surface you'll find another interface with similar character and distribution that was buried mid-February. This layer has been reactive in recent snowpack tests and has produced large avalanches, particularly in the south of the region where the overlying slab has become deep and cohesive. There are several persistent weak layers that are showing signs of improvement but still remain suspect as low probability - high consequence avalanche problems. Two surface hoar layers buried in January are now 100-150 cm below the snow surface. Deeper in the snowpack (150 - 200 cm deep) is a facet/crust/surface hoar layer buried in December. Near the base of the snowpack is a crust/facet combo layer buried in late November. These layers may "wake-up" with strong inputs such as solar radiation, rapid loading/warming, or a cornice fall. Human triggering is also possible in shallow, rocky terrain.