Watch for uncharacteristic wind slabs at upper elevations as east winds continue. Uncertainty about triggering large avalanches warrants careful terrain selection. Read about managing these conditions in this forecaster blog.
An uptick and shift to easterly winds on Thursday formed new wind slabs at upper elevations that will likely remain sensitive to human triggers. Given the recent variability in wind direction and unusual loading pattern, treat all aspects as suspect. Cornices may be reaching their breaking point.
Despite decreasing avalanche danger, 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.
FRIDAY NIGHT: Clear, light to moderate east wind, alpine temperatures around -17 C.
SATURDAY: Sunny with a few clouds, light to moderate east wind, alpine temperatures around -16 C.
SUNDAY: Mix of sun and cloud, light south wind, alpine temperatures around -16 C.
MONDAY: Mix of sun and cloud, light variable wind, alpine temperatures around -12 C.
Reports of avalanches on Friday consisted of of 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 on Thursday offers a helpful visual of this avalanche activity. Operators continue to report numerous small dry loose avalanches.
There has been recent notable avalanche activity in and around Glacier National Park. On Friday, observers reported a large (size 2.5) natural avalanche on a southeast aspect in the alpine, breaking on a facet crust layer buried Jan 24th. Similarly, on Wednesday, there were two large (size 2.5-3) human-triggered avalanches reported just outside of Glacier National Park on south and west facing alpine slopes (MIN report), also failing on the persistent weak layer.
Last weekend and earlier this week, there were numerous reports of persistent slab avalanches across the region, including some in lower elevation cutblocks in the southern Selkirks (here and here), a wind slab on a southeast aspect that stepped down to a deeper layer to produce a size 3 avalanche on London Ridge, and a size 1.5 skier triggered slab near Revelstoke (MIN report).
On Thursday, winds picked up out of the east/northeast with enough gusto to move snow around, giving new life to wind slab problems in the region. Watch for wind slabs in uncharacteristic places at upper elevations as easterly winds continue.
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 below treeline. On steep south facing terrain this layer may consist of facets on a sun crust. This persistent weak layer has potential to surprise backcountry users with how wide the fracture can travel across slopes. This layer will be slow to gain strength and requires careful terrain selection. The mid/lower snowpack is generally strong and settled in most areas.
