Human triggering of sensitive weak layers is likely. Careful evaluation of the snowpack is required for safe travel.
Weather Forecast
Cloudy with sunny periods and isolated flurries bringing trace amounts of precipitation today. Alpine temperatures will be steady around -8 with freezing levels reaching 1000m. A series of fronts continues to bring light snow to Rogers Pass through the weekend, with 4cm on Saturday, 9cm on Sunday and 7cm on Monday. Expect Moderate SW Winds.
Snowpack Summary
Around 30cm of new storm snow sits atop the January 16 surface hoar layer. Warm temps and mod-strong S-SW has contributed to slab formation in the upper snowpack. The December 15 surface hoar is approximately 100cm down and is highly visible in profiles. This deeper instability is still producing sudden planar results in stability tests.
Avalanche Summary
A natural avalanche cycle accompanied strong winds yesterday morning with several size 2-3 avalanches occurring in steep north facing alpine paths.
Confidence
Intensity of incoming weather systems is uncertain
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.