Yet more surface hoar on Donner Summit

Location Name: 
W ridge Castle Pk
Date and time of observation: 
Mon, 01/11/2016 - 12:30
Location Map: 
United States
39° 21' 54.0756" N, 120° 21' 32.2488" W
See map: Google Maps
US


Red Flags: 
Whumphing noises, shooting cracks, or collapsing
Observation made by: Guide at Donner Summit Avalanche Seminars
Snowpit Observations
More detailed information about the snowpack: 

We performed 12 CTs across a NNW slope early this afternoon with very consistent results across 5 different snow pits.  Clean planer breaks approx 6 cm and 18 cm below snow surface. Both breaks occured within first 10 taps (CTE, several CT1).  The upper break was on SH just below a very thin, weak crust (rc?); the lower break on an unidentified grain type (maybe SH, difficult to conclusively ID).  We tested propagation of these layers on a non-standardized propagation column 30 cm by 200 cm with none of the layer failures breaking the length of the column.  Aslo, an RB6 partial block failing on the lower layer.  Photos show removing snow after CT-revealed layer fractures; our long propagation column; and today's (last night's) new SH layer.  HS in the area averaged 230 cm.  Even with a day-long strongly targeted approach we could not initiate any subsurface collapses on areas with strong SH development... until the very end of our tour (1500) when a skier turning hard to stop on the shady edge of a sloping open glade caused an approx 5 m diameter collapse that resulted in surface deformation.  No  other signs of instability noted.

Snowpit or crown profile photo or graph: 
Snowpack photos: 
Weather Observations
Blowing Snow: 
Air temperature: 
Wind Speed: 
Calm
Precipitation: 
Air temperature trend: 
Warming
Wind Direction: 
Accumulation rate: 
More detailed information about the weather: