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 60-100 cm deep throughout the region.
MONDAY NIGHT: Mostly cloudy, isolated flurries with a trace of snow, light west wind with moderate gusts at ridgetop, alpine temperatures around -14 C.
TUESDAY: Cloudy, light flurries with a trace of snow, light west wind with moderate gusts at ridgetop, alpine temperatures around -12 C.
WEDNESDAY: Cloudy, light flurries with a trace of snow, light west wind with moderate gusts at ridgetop, alpine temperatures around -12 C.
THURSDAY: Mix of sun and cloud, light south wind with strong gusts in the afternoon, alpine temperatures around -11 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 2000 m that broke 15-50 cm deep. This MIN report from near Eagle Pass offers a helpful visual of this avalanche activity. Operators have also reported numerous recent dry loose avalanches (size 1-1.5).
Observations of avalanches on the late January persistent weak layer continue to trickle in. This MIN report from the Gorge on Friday is a helpful example of the lower elevation slopes where the surface hoar has been preserved. On Friday, operators reported a large (size 2.5) natural avalanche on a southeast aspect in the alpine, releasing on the facet layer. Similarly, last week, there were two notable 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 a combination of facets with a crust. Over the past week the persistent slab problem has produced fewer avalanches than in the first week of February, but is still showing signs of instability and warrants careful assessment.
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. 60-100 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.
The mid/lower snowpack is generally well settled and strong.
