Fresh wind slabs were formed by moderate to strong northeast wind at all elevations. The sun is strong at this time of year and can weaken the snowpack and make it easier to trigger buried weak layers which have surprised people.
A weak layer of surface hoar is buried 60-100 cm deep. Even though avalanche reports decreased over the past week it might still possible to human-trigger. The distribution of this problem extends to all aspects and elevations, but north to east aspects near treeline have been a hot-spot for reactivity.
Moderate to strong northeast wind formed wind slabs at all elevations which are reactive to human triggers.
The recent storm snow may sit on a weak layer of surface hoar at treeline and below and a sun crust on steep solar aspects. With warming temperatures and solar input slab properties of the recent storm snow might increase and make it more likely to trigger slab avalanches on this weak layer.
Saturday night: Clear, light northeast wind, alpine high temperature -22 C, freezing level at valley bottom.
Sunday: Sunny, light northeast wind, alpine high temperature -15 C, freezing level at 500 m.
Monday: Sunny, light north wind, alpine high temperature -7 C, freezing level at 1000 m.
Tuesday: Mostly sunny, light northeast wind, alpine high temperature -5 C, freezing level at 1500 m.
Numerous slab avalanches up to size 2.5 and many small dry loose avalanches were reported during and after the storm mid week. Many of these avalanches released on the old snow surface consisting of a weak surface hoar layer or sun crust on steep solar aspects which the new storm snow covered. Even though reports of avalanches releasing on that layer have decreased it might still be possible for humans to trigger.
Reports of large (size 2-3) human-triggered and explosive-triggered avalanches releasing on the February 22 surface hoar layer continued over the past week from operators region-wide. This layer continues to surprise people with remote-triggered activity, wide propagation, and a false sense of stability from unreactive ski cuts or from multiple people moving through the terrain before an avalanche releases. Observations have extended to all aspects and elevations, but north to east aspects near treeline have been a hot-spot for reactivity. Avalanches have also occurred at unusually high elevations for surface hoar, with several cases of wind slabs stepping down in the alpine. While the number of reported avalanches has decreased, the size has increased, with more of the activity releasing size 2+.
Moderate to strong northeast wind has redistributed the snow and formed wind slabs reactive to human triggers. The snow surface varies from soft snow and wind pressed in the alpine and at treeline to sun crust on steep solar aspects. The recent snow may sit on a surface hoar layer and a sun crust on steep solar aspects. This layer is responsible for many avalanche releases and might develop into a persistent weak layer.
A widespread weak layer of surface hoar is buried 60-100 cm deep. On solar aspects, this layer may sit over a crust. This persistent slab problem has transitioned into a low probability/high consequence scenario. If triggered, avalanches will be large and getting caught could have serious consequences. Managing this problem requires a patient and diligent mindset, implemented by avoiding suspect slopes and maintaining conservative terrain margins. This persistent weak layer will likely pose the threat of a low probability/high consequence avalanche until there is a substantial change in the snowpack. Read more about surface hoar on our forecaster blog.
