A spicy persistent slab problem is not showing any signs of letting up. Don't get complacent about considerable danger. Avalanches have been large and human triggering remains likely.
Incremental snowfall and strong winds are building reactive wind slabs in the alpine and open areas at treeline. A natural wind slab cycle size 2-3 was observed Tuesday. If triggered, windslabs have the potential to trigger deeper weak layers.
A weak layer of surface hoar sits 40-70 cm deep. Read more about surface hoar on our forecaster blog! Human triggering of this layer is very likely, and has been observed extensively through the region over the last few days even as professionals seek to actively avoid suspect terrain features (eg. convex rolls). Observations are from all aspects and elevations, but especially concentrated on north to east aspects around treeline.
Wednesday night: A trace of new snow. Moderate southwest wind. Freezing level valley bottom.
Thursday: 5-10 cm new snow. Strong southwest wind. Freezing level 1500 m.
Friday: 10-20 cm new snow. Light southwest wind. Freezing level 1100 m.
Saturday: 5-10 cm new snow. Light variable wind. Freezing level valley bottom.
We've been flooded with reports of persistent slab avalanche activity on the February 22 surface hoar since Saturday, with no signs of slowing down. A natural cycle was observed Monday and Tuesday, with several cases involving cornice fallstriggering wind slabs which stepped down to persistent slabs, size 2-4.
A deluge of skier triggered and remote triggered avalanches, size 1-2 have been reported by nearly every ski operation region wide even as professionals tiptoe around, avoiding suspect terrain features. The problem is touchy but tricky, in many instances, slopes were ski cut with no results, only to have the third or fourth skier in the group accidentally trigger the slab.
Observations are from all aspects and elevations, but especially concentrated on north to east aspects around treeline. They are also occurring at unusually high elevations for surface hoar.
Incremental snowfall and strong winds are building reactive wind slabs in the alpine and open areas at treeline.
A weak layer of widespread surface hoar sits 40-70 cm deep. It may sit over a crust on solar aspects. The overlying snow has been cohered into slabs by incremental loading through successive storms, wind and mild temperatures. As slab character and depth increase, so do reactivity and size of avalanches failing on the weak layer. Read more about surface hoar on our forecaster blog!
