Shifting Winds, Cornices, Sluffs, and Deep New Snow on Castle

Location Name: 
Castle Peak and Andesite Ridge
Region: 
Donner Summit Area
Date and time of observation: 
Tue, 03/08/2016 - 13:30
Location Map: 
United States
39° 21' 53.244" N, 120° 21' 32.184" W
See map: Google Maps
US


Red Flags: 
Recent avalanche activity
Recent loading by new snow, wind, or rain
Observation made by: Forecaster
Snowpit Observations
More detailed information about the snowpack: 

100 to 150 cm of new snow was present in non wind loaded areas on Castle Peak and Andesite Ridge with the higher amounts of new snow in areas above 8000 ft. In wind loaded areas, new snow depths reached 160 to 190 cm. Snowpit tests did show several weaknesses within the storm snow, but none of the fractures that started on these weaknesses would propagate across a column during Extended Column Tests performed on wind loaded test slopes along the west ridge of Castle Peak (ECTN 9, ECTN 10, ECTN 12, ECTN 14, ECTN 22, ECTN 28 - See photo #1 for one set of tests @ 8300 ft. @ the coordinates attached to this observation). Below the new snow the old snow surface remains wet up to at least 8500 ft. Ski cuts and large refrigerator sized cornice pieces dropped on wind loaded test slopes on Castle Peak and on Andesite Ridge did not trigger any shooting cracks. On some of the steeper wind loaded test slopes these large cornice pieces did trigger small loose dry snow sluffs that involved the top 15 to 20 cm of the new snow. Evidence of previous avalanche activity that likely occurred during the storm did exist on many of these test slopes. Evidence of wind loading existed on most aspects and some evidence of wind scouring also existed on some of the N-NE-N aspects. 

Ski cuts on non wind loaded test slopes in below treeline terrain also did not trigger any shooting cracks or failures other than some minor sluffing. A thin breakable sun crust did form on the E-SE-S-SW aspects during the morning before thick cloud cover obscured the sun by 11:30 am.  

Photo 1: ECTN's on a N facing wind loaded test slope at 8300 ft. at the coordinates attached to this observation. 39.36479, -120.35894

Photo 2: Cornices pointing opposite directions (both E and W) on Andesite Ridge indicating shifting winds and wind transport 39.354237, -120.366210 

Photo 3: Full cloud cover across the area by 12:30 pm.

Photos 4 and 5: Loose dry snow sluffs triggered by intentional cornice drops #4 on the west ridge of Castle at 8300. ft near the ECT photo above and #5 on Andesite Ridge at 39.350785, -120.365996.

Snowpack photos: 
Weather Observations
Blowing Snow: 
Yes
Cloud Cover: 
100% of the sky covered by clouds
Air temperature: 
Below Freezing
Wind Speed: 
Moderate
Precipitation: 
Snow
Air temperature trend: 
Cooling
Wind Direction: 
Southwest
Accumulation rate: 
Less than 1 in. per hour
More detailed information about the weather: 

Full cloud cover moved into the area around 11:30 and light snow flurries started around 12 and continued through the afternoon.