Natural and human triggered wind slabs in Negro Canyon.

Location Name: 
Negro Canyon
Region: 
Donner Summit Area
Date and time of avalanche (best estimate if unknown): 
Sun, 01/22/2017 - 11:20
Location Map: 
United States
39° 20' 30.5772" N, 120° 17' 31.6716" 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
Avalanche Observations
Avalanche Type: 
Dry
Slab
Crown Height: 
2 ft
Aspect: 
Northeast
Weak Layer: 
Storm Snow
Terrain: 
Near Treeline
Bed Surface: 
Storm Snow
Number of similar avalanches: 
2
More detailed information about the avalanche: 

Natural and intentionally human triggered wind slab avalanches occurred today in wind loaded near treeline areas on the observed NE-E-SE aspects in this area. Crown heights of 2 feet were observed. Both natural avalanches appeared to have been triggered by cornice collapse. The intentional human trigger was done so remotely by moving out onto a wind pillow features adjacent to corniced test slopes. The remote trigger occurred from the spot the photo was taken. Slope angle on failed test slope was 38 degrees.

Skier triggered cracking was limited to wind affected areas. Most cracks were short at less than 3 feet in length, but the crack that caused the remote trigger extended 30 to 50 feet away from the skier both up and down the ridge. Only a short portion of this crack was cornice collapse and was well away from the spot of initiation.

Stiff, higher density surface snow was prominent in both wind exposed and wind protected areas. A notable upside down storm snow structure of higher density snow from today on top of lower density snow from yesterday was easily felt with skis and poles.

Avalanche Photos: 
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: 
Static
Wind Direction: 
Southwest
Accumulation rate: 
Less than 1 in. per hour
More detailed information about the weather: 

Most of the morning held 100% cloud cover with a break for about 20 min. Periods of light snowfall and no snowfall led to little additional accumulation during the morning hours.