Avalanche Activity in Negro Canyon

Location Name: 
Negro Canyon
Region: 
Donner Summit Area
Date and time of avalanche (best estimate if unknown): 
Thu, 03/24/2011 - 11:00
Location Map: 
United States
39° 20' 42.9324" N, 120° 17' 38.4504" 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
Observation made by: Professional Observer
Avalanche Observations
Avalanche Type: 
dry,slab,
Weak Layer: 
Storm Snow
Elevation: 
7 200ft.
Bed Surface: 
Storm Snow
More detailed information about the avalanche: 

The storm was picking up intensity by mid morning with increasing SW winds to the strong + range.  These winds were moving intense amounts of snow.  Visibility was very limited to about 200-300' and much less in wind exposed open locations.  There were many signs of instability within the storm snow; cracking and shooting cracks, recent natural avalanche activity, and remote triggering of cornices and slabs.  Cornices are built out large and are very sensitive.  Exposed terrain is wind effected and dense.  

Photos are hard to make out in flat light conditions.

Photo #1:  Shooting cracks from skis were common in wind loaded terrain. 

Photo#3:  Remotely triggered cornice failure from 40' away on ridgeline.  This cornice failure triggered a slab avalanche, 2' crown, that ran down the gulley 250-300'.  NE aspect, 7300', 38 degrees.  The cornice block that failed is in the foreground with part of the crown line up slope and behind remaining cornice.

Photo #4:  The gully avalanche path with debri.

Photo#5:  Natural avalanche, 1-1.5' crown, occured sometime earlier morning around first light and was partially covered up.  East aspect, 7200', cross loaded small gully feature, 35 degrees.  Slide ran for 200' into low angle terrain.

Avalanche Photos: 
Avalanche observation video: 

negrocanyon2011 3 24 007

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: 

At 10:30am SW winds began to increase to strong and extreme.  Snowfall intensity also increased to over 1''/hour.