South Columbia

The stormy weather tapers off on Wednesday but the tricky storm slab problem is likely to persist for several days. Use a very conservative approach to terrain selection and stick to mellow, low-consequence areas.

Low - Due to the number of field observations

One more storm system is expected to bring another punch of precipitation for Wednesday before conditions ease on Thursday and Friday. There is some model disagreement with respect to snowfall amounts for the region on Tuesday overnight and Wednesday with another 15-40cm of snowfall is possible. Freezing levels are expected to be around 1500m and alpine winds are forecast to be strong from the SW. On Thursday, unsettled conditions are expected with sunny breaks possible in the morning and light snowfall in the afternoon. Freezing levels are expected to fall to around 1000m and alpine winds should be light from the SW. Friday should see similar conditions with light intermittent snowfall, freezing levels below 1000m, and light alpine wind.

On Sunday and Monday, several natural and human-triggered avalanches were reported up to size 2.5. These storm slabs were typically 50-80cm thick and occurred on all aspects and elevation bands. Of particular concern were three remotely triggered avalanches, the furthest being triggered from 150m away. This suggests that the storm slab is gaining cohesion and the propagation potential of the underlying weak layer is increasing. A widespread natural cycle is expected to have occurred on Tuesday but there was no information at the time of publishing. Touchy storms slab will continue to be sensitive to human-triggering at all elevations on Wednesday, especially at higher elevations where the snow remains dry. Remote-triggering may still be a concern, especially below 1800m where the surface hoar layer is most reactive.

On Tuesday, freezing levels climbed to around 2000m and rain likely soaked the snow surface creating upside-down conditions at lower elevations. At higher elevations where the precipitation fell as snow, it is continuing to add to a storm slab that is typically around 60-100cm thick. This storm slab sits over the early-Dec interface which consists of large surface hoar below 1800m, sun crusts on south-facing slopes, old wind affected surfaces above treeline, and possibly faceted surfaces in some areas. This interface appears to be quite variable throughout the region and information on this layer has been limited, so treat the layer with extra respect until more info is available and give the storm snow time to stabilize. Strong SW winds continue to build thick wind slabs in leeward features at alpine and exposed areas at treeline. Deeper in the snowpack, the surface hoar interface from early November have been dormant but still may wake up with heavy loading or smaller avalanches stepping down. On very high northern aspects, a crust/facet interface may be found near the ground.