Watch for wind slabs in unusual places as winds shift again, this time to the south. Uncertainty about triggering large avalanches warrants careful terrain selection. Read about managing these conditions in this forecaster blog.
Shifting winds from north to east to south have formed a complex pattern of wind slabs at upper elevations that will likely remain sensitive to human triggers. 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.
SATURDAY NIGHT: Mostly cloudy, light southeast wind, alpine temperatures around -17 C.
SUNDAY: Cloudy with sunny breaks, light south wind, alpine temperatures around -16 C.
MONDAY: Mix of sun and cloud, light variable wind, alpine temperatures around -12 C.
TUESDAY: Cloudy, light west winds with moderate gusts at ridgetop, isolated flurries with trace accumulations, alpine temperatures around -13 C.
Operators on Friday reported small to large (size 1-2) wind slab avalanches near treeline and above as a result of moderate east winds. This MIN report from neighboring Glacier National Park offers a helpful visual of this avalanche activity. There continue to be reports of small dry loose avalanches.
Observations of avalanches on the late January persistent weak layer continue to trickle in. This MIN report from Friday shows that the surface hoar remains alive and well 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 are forecast to shift to a new direction overnight (southeast) and again tomorrow (south) and may form fresh wind slabs in lee features at upper elevations. Previous winds blew from the east/northeast with enough gusto to move snow around and build reactive wind slabs. Watch for these wind slabs in unusual places as tricky cross-loading and reverse-loading continues.
While wind may be forming slabs in lee features, 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 requires careful terrain selection.
The mid/lower snowpack is generally strong and settled in most areas.
