Sherwins - New snow instabilities

SNOWPACK OBSERVATION
Sherwins
Submission Info
Forecaster
Wednesday, December 4, 2019 - 12:00pm
Red Flags: 
Recent avalanche activity
Recent loading by new snow, wind, or rain
37° 36' 30.7584" N, 118° 59' 27.8124" W
Snowpit Observations
More detailed information about the snowpack: 

Toured today in the Sherwins.  Snowing moderately most of the day resulting in new storm snow instabilities in the form of wind slabs just below upper ridgeline and storm slabs mid-slope in steep convexities.  Triggered one 8-10" soft storm slab avalanche (~25' wide, running ~150ft) while ski cutting convex roll above steep mid-slope terrain.  Click here for more info. Ski cut slope just below ridgeline above Mammoth Rock Bowl resulting in 8-10" fracture 10-15' across slope.

 First pit dug ~50ft below the ridgeline in the hose area to investigate interesting and suprisingly firm old surface layer (wind slab combined perhaps with small cornice collapses that swept soft snow away) extended down slope ~75ft.  This thin pencil hard was inpenetrable with skis, had ~15cm of new snow from today covering it, and sitting above a 4Finger layer.  2 Extended column tests failed and propogated just below this firm layer.  EXTP 16 & 18.  See attached profile.  I felt this layer would become more concerning as the day progressed and more snow accumulated ontop of this layer, where a skier could hit a weak spot and result in an avalanche.  

Second pit dug in an exposed shallow area above Mammoth Rock Bowl where fresh wind slab was developing.  CT tests failed easily just below thin fresh windslab, and moderately below a slightly older and deeper wind slab.  See attached profile.  

 

Snowpit or crown profile photo or graph: 
Weather Observations
More detailed information about the weather: 

Snowing moderatly most of the day, with 8-10" of accumulation by early afternoon (1:30pm).  Calm winds, except at very ridgetop where winds were consistently moderate out of the SW and quite unpleasant.  Relatively warm, -1.5°C at noon at 10,000'.  Above freezing at 8500'.  

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