Watch for wind slabs in unusual places. These slabs have potential to break wider than expected and may be slow to bond. Read about managing these conditions in this forecaster blog.
Shifting winds from all compass directions in the past week have formed a complex pattern of wind slabs at upper elevations that may be possible to trigger. Given the potential for cross-loading and reverse-loading, treat all aspects as suspect. Cornices may be reaching their breaking point.
It remains possible to trigger persistent slab avalanches in isolated steep terrain features. The primary layer of concern is layer of surface hoar, facets, and/or crusts buried 60-120 cm deep throughout the region.
MONDAY NIGHT: Cloudy, isolated flurries with trace accumulations, light northwest wind with moderate gusts at ridgetop, alpine temperatures around -14 C.
TUESDAY: Cloudy, light northwest winds with moderate gusts at ridgetop, isolated flurries with trace accumulations, alpine temperatures around -11 C.
WEDNESDAY: Cloudy, light northwest winds with moderate gusts at ridgetop, isolated flurries with trace accumulations, alpine temperatures around -11 C.
THURSDAY: Mix of sun and cloud, light south winds with moderate to strong gusts in the afternoon, alpine temperatures around -10 C.
Over the weekend, numerous small to large (up to size 2) natural and human-triggered wind slab avalanches were reported across a wide range of aspects above 2100 m that broke 10-50 cm deep. These MIN reports, both from Mt. Brennan on Saturday (here and here), offer helpful examples of this avalanche activity. There continue to be reports of small (size 1-1.5) dry loose avalanches.
Observations of avalanches on the late January persistent weak layer continue to trickle in. This MIN report from Joss Mountain on Friday shows that the surface hoar remains reactive on lower elevation cutblock features. Last week, a wind slab on a southeast aspect was thought to step-down to the late January crust/facet interface to produce a size 3 avalanche on London Ridge, and there was a size 1.5 skier triggered slab near Revelstoke (MIN report).
Winds have varied in strength and direction over the past week, loading cornices and forming wind slabs at upper elevations that may still be possible to trigger. Watch for these wind slabs in unusual places as complicated cross-loading and reverse-loading patterns are prevalent. Wind slabs may overlie weak, sugary, faceted snow, meaning that they could break wider than expected and will likely be slow to bond.
In wind-sheltered areas, the upper snowpack is becoming soft and faceted with the cold temperatures. 60-120 cm of snow from February is settling over a weak layer of surface hoar that has shown reactivity at treeline or in "treeline-like" features, like cutblocks, below treeline. On steep south-facing terrain, this layer may consist of facets on a sun crust. This persistent weak layer will be slow to gain strength and warrants careful terrain selection.
The mid/lower snowpack is generally strong and settled in most areas.
