South Columbia

The weather is improving but lingering storm slabs will remain sensitive to human-triggering for several days. Conservative route selection is still critical.

Moderate - Due to the number of field observations

Unsettled conditions are expected on Thursday with sunny breaks in the morning and light snowfall in the afternoon. 5-10cm of snowfall is likely with freezing levels around 1000m. Alpine winds are forecast to be moderate from the SW. On Friday, mainly dry conditions are expected with a mix of sun and cloud. Freezing levels should be around 800m and alpine winds should be light. A weak Pacific storm system may spill into the interior region on Saturday bringing light snowfall.

Observations have been limited during the storm, especially from alpine elevations. On Monday, and Tuesday several natural and human-triggered storm slab avalanches were reported up to size 2.5. These storm slabs were typically 30-60cm thick and occurred on all aspects and elevation bands. Also reported were two very large wet slab avalanches but details were limited, likely due to visibility. Storm slabs are expected to remain sensitive to human-triggering on Thursday but natural activity should taper off now that the storm has ended. The exception might be steep sun-exposed slopes if the sun makes a longer appearance than expected.

Over the past week, 60-100cm of storm snow has typically accumulated in the region. On Tuesday, rain affected the snow surface as high as 2000m but new snow has subsequently fallen as low as 1500m. The 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 extra time to stabilize. Recent strong SW winds have built thick wind slabs in leeward features at alpine and exposed areas at treeline. Deeper in the snowpack, the surface hoar interface from early November has 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.