Fragile Wind Slabs, Large Cornices, ECTP's, and Wet snow on Castle Peak and Andesite Ridge

Location Name: 
Castle Peak and Andesite Ridge
Region: 
Donner Summit Area
Date and time of observation: 
Sat, 03/12/2016 - 12:15
Location Map: 
United States
39° 21' 55.3176" N, 120° 21' 28.8468" W
See map: Google Maps
US


Red Flags: 
Recent avalanche activity
Whumphing noises, shooting cracks, or collapsing
Recent loading by new snow, wind, or rain
Obvious avalanche path
Observation made by: Forecaster
Snowpit Observations
More detailed information about the snowpack: 

6 to 10 inches of new snow had fallen on Castle Peak and Andesite Ridge during the last 24 hours.. This new snow rested on top of wet snow and breakable crusts below 7800 ft. and on top of other recent snow above 7800 ft. A thin graupel layer existed at the base of the new snow in some areas. Ski cuts on test slopes, hand pits, and general observations did not show signs of instability in the sheltered non-wind affected below treeline areas as of 2 pm today. On near and above treeline leeward slopes wind slabs 12 to 18 inches deep existed, and tests on these wind slabs showed them to be fragile on some slopes. A refrigerator sized piece of cornice dropped onto one NW facing test slope at 8400 ft. at 39.365365, -120.358013 triggered a 12 to 16 inch deep wind slab fracture on the test slope. Snowpit tests on this slope yielded unstable results at the same depth on a graupel layer at the base of last night's new snow (ECTP 17 and ECT30). Other cornice pieces dropped onto less wind loaded E and SE facing slopes did not trigger wind slab failures. On of the cornice pieces dropped onto a wind loaded slope on Andesite Ridge triggered a wind slab avalanche. Click here for the details.

Photo: Refrigerator sized cornice piece dropped onto this 38 to 40 degree NW facing test slope at 8400 ft. triggered a 2 to 16 inch deep wind slab fracture. 

Video: ECTP 30 on the graupel layer at the base of the wind slab that formed last night and today on the same test slope on the other side of the remaining cornice. Previous to this video we recorded an ECTP 17 on at the same depth. 

Video 2: Active wind transport, wind loading and cornice formation along the Castle Peak ridge. 

Snowpack photos: 
Snowpit videos (tests, etc): 

Wind Slab Failure, Large Corinces, and ECTP's on a Test slope on Castle Peak

Wind Loading on Castle Peak

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

Snow started increasing in intensity at 1 pm, and increased to about 1 in/hr rates above 7500 ft.