South Columbia

Watch for the rapid formation of potentially touchy wind slabs as warm southwest flow starts to take hold of the region. Conditions are expected to deteriorate this weekend as the warm storm pushes inland, more details in the latest forecaster blog.

Southwest flow ushers in plenty of wind, moisture and a rising freezing level.

THURSDAY NIGHT: Freezing level at valley bottom, light to moderate southwest wind, 1 to 4 cm of snow possible.

FRIDAY: Overcast, freezing level at or near valley bottom, light to moderate west/southwest wind, 1 to 6 cm of snow possible during the day with another 1 to 3 cm possible Friday night.

SATURDAY: Overcast, freezing level beginning at valley bottom rising to about 1000 m, light to moderate southwest wind, 2 to 4 cm of snow possible during the day with 2 to 10 cm Saturday Night.  

SUNDAY: Overcast, freezing level beginning around 600 m climbing to about 1500 m during the day, strong to extreme southwest wind, 5 to 10 cm of snow at upper elevations with rain in the valleys. 7 to 12 more cm of snow expected at upper elevation Sunday night.

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.  

In the adjacent Glacier National Park Region there were some large natural wind slab avalanches reported from extreme north facing terrain features on Monday. A similar natural avalanche from extreme terrain was reported from the southern portion of this region on Monday too.

On 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 warrants assessment. This MIN report from Joss Mountain last Friday shows that the surface hoar remains reactive on lower elevation cutblock features.  

10 to as much as 30 centimetres of light density snow now rests on a variety of surfaces including sugary facets, feathery surface hoar, and wind-affected snow that formed as a result of the recent cold, dry and windy weather. 

Southwest wind is expected to increase as we head towards the weekend, it's difficult to pin down exact timing, but once it starts to blow touchy wind slabs are expected to form quickly and will likely be slow to heal as they rest on weak, sugary, faceted snow. Winds have varied in strength and direction over the past week, loading cornices and forming wind slabs at upper elevations. Watch for stiff wind slabs in unusual places as complicated cross-loading and reverse-loading patterns are prevalent. 

60-120 cm of snow from February is settling over a layer of surface hoar buried in late January. Reactivity on this layer has primarily been observed at treeline and in "treeline-like" features, like cutblocks, that are below treeline. On steep south-facing terrain, this layer may consist of facets on a sun crust, which has produced notable low probability/high consequence avalanches and requires a conservative approach. 

The mid/lower snowpack is generally well settled and strong.

• Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
• Approach lee and cross-loaded slopes with caution.
• Be aware of the potential for large avalanches due to the presence of a persistent slab.
• Extra caution is needed around cornices under the current conditions.