South Columbia

Fair - Forecast snowfall amounts are uncertain on Tuesday

The ridge of high pressure that moved into the interior on Sunday is expected to continue to persist on Monday bringing clear skies and freezing levels near valley bottom. The next system moving in from the Northwest coast looks very similar to the one we just experienced. It looks like precipitation will start in the Cariboo and North Monashee by early Tuesday. The freezing level is expected to rise to about 1000 metres by early Tuesday, and then to start to fall back to the surface by late afternoon. This is a fast moving system with forecast alpine elevation winds from the Northwest in the 50-70 km/hr range. A trailing cold front will continue to bring precipitation into Wednesday morning. I expect the North and West Monashee to get the most precipitation, and the South Selkirk and Purcell to get the least.

Natural avalanches up to size 2.0 were observed on Saturday in the Monashees and Selkirks releasing in the storm snow as soft slabs or loose snow sluffing. Most were 20-30 cm deep, and some were commented to be running fast and long in moderate angled terrain. With higher than forecast new snow overnight into Sunday, we expect that a natural cycle occurred in areas where the storm slab has approached 50 cm. The next wave of precipitation may be the "Tipping Point" for areas that currently have a 20-30 cm storm slab.

Some areas of the North Columbia received up to 30 cm on Saturday. The North and West Monashee received an additional 20 cm on Saturday night. Strong southwest winds and warm temperatures have created wind slabs on North through East aspects in the alpine and at treeline. The storm slab at treeline is approaching 50 cms and has been reported as very reactive to human triggers. The East and South ranges of the Interior Mountains have been much drier. The storm slab in the Purcells is closer to 20 cm in most places.The new snow load is building faster in the northern ranges of the interior than it is in the southern and eastern ranges. The depth of the new storm snow above the various old surfaces is what is driving the danger ratings at this time. Large surface hoar and near surface facets are widespread above various crusts and hard wind slabs. Some areas have a sun crust in the alpine on steep south and west aspects. There is a rain crust that is buried between 40-55 cm in some areas that reaches up to about 2200 metres. The mid-pack is reported as generally strong and well settled. Observers are still able to find the early November surface hoar layer. This layer has not been reactive during the recent long dry spell. Tests show that it is getting harder to pull the snowpack apart at this interface. We may still see this layer become active again if we get the right combination of load and warm temperatures. Going down deeper, we still need to consider the interface between the snow that did not melt over the summer, the glacial ice, and the October rain event. If this deeply buried beast wakes up, we may see very large avalanches in high alpine north and northeast aspects