A conservative approach is prudent as conditions deteriorate today. Wind and new snow are coming together to form fresh storm slabs at upper elevations, be careful that great riding doesn't lure you into complex terrain. Read more in the latest forecaster blog.
A persistent weak layer buried 60 to 120 cm deep has produced recent large avalanches and is expected to become increasingly reactive this weekend. This layer has been most sensitive around treeline, but may also extend into alpine terrain and/or down into the trees. Avalanches failing on this interface will be large and destructive.
Watch for the formation of touchy storm slabs at all elevations, even in the trees. 20 to 60 cm of recent snow rests on an untested mix of nasty weak layers which include surface hoar, facets, crust and firm old wind slabs. Human triggering of these slabs is likely and storm slabs in wind exposed terrain may be quite sensitive. This problem is expected to get worse as we move through the weekend.
Southwest flow takes aim at the province this weekend delivering plenty of precipitation and warm temperatures.
FRIDAY NIGHT: Freezing level at valley bottom, light southwest wind at most elevations with strong west wind at ridgetop, 3 to 6 cm of light density snow expected.
SATURDAY: Overcast, freezing level beginning at valley bottom rising to about 1000 m, moderate west wind at most elevations with strong west/northwest wind in the higher alpine terrain, 4 to 10 cm of snow expected during the day with another 2 to 5 cm Saturday night.
SUNDAY: Overcast, freezing level beginning near valley bottom rising to about 1500 m, moderate southwest wind at treeline with strong to extreme southwest wind in the alpine, 5 to 15 cm of snow possible at upper elevations with rain in the valleys. 5 to 15 cm of snow is expected at upper elevations Sunday night.
MONDAY: Overcast, freezing level beginning around 1500 m and holding there throughout the day, strong southwest wind, 5 to 10 cm of snow at upper elevations with rain in the valleys.
On Friday strom slabs began to form and were sensitive to human triggering, especially in areas kissed by the wind. This MIN from Friday in the neighboring North Columbia region is a great example of that activity.
A size 2.5 skier triggered avalanche was reported near Revelstoke Wednesday on a steep west facing slope around 1600 m. In the Gold Range a skier remote triggred a size 1.5 wind slab avalanche on an east facing feature at 2200 m. These are great examples of the strange conditions created by reverse wind loading and may be a portent of things to come as the weekend trends warm and stormy.
Last Saturday, there was a notable MIN report of a human-triggered wind slab on a southeast aspect in the alpine that stepped-down to deeper persistent weak layers to produce a very large avalanche that ran full path and destroyed mature timber.
The second week of February produced fewer persistent slab avalanches than the first week of February. But, the late January persistent weak layer is still showing signs of instability and a conservative approach is critical as this storm begins to add weight to it. This old MIN report from Joss Mountain is a helpful example of the lower elevation slopes where the surface hoar has been preserved and may reactivate this weekend.
Southwest flow has started pushing some more serious precipitation our way. As of Friday afternoon the first wave of the storm has produced about 25 cm or so near Revelstoke but less snow further south. London Ridge has only received 13 cm in the last 24 hours and areas around Kaslo are showing less than 10 cm so far. There is now 20 to 60 cm of snow resting on an untested potpourri of weak layers including sugary facets, feathery surface hoar, and wind-affected snow that formed as a result of the cold, dry and windy drought period.
We've now got 70 to 130 cm of snow above the late January persistent weak layer which is composed of surface hoar. This layer is most prevalent at treeline and in "treeline-like" features such as cutblocks. On steep south-facing terrain, this layer may consist of facets on a sun crust, which has produced very large low probability/high consequence avalanches.
