Natural Avalanche on Wildflower Ridge

Location Name: 
Mt. Judah
Region: 
Donner Summit Area
Date and time of avalanche (best estimate if unknown): 
Mon, 12/17/2012 - 08:00
Location Map: 
United States
39° 18' 26.2836" N, 120° 19' 6.5136" 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,
Avalanche Width: 
300ft.
Avalanche Length: 
80ft.
More detailed information about the avalanche: 

Very warm conditions this morning with gale force winds on Donner Summit.  Visibility was very poor and little could be observed in the field.  There was a large natural avalanche on Wildflower Ridge that was cornice triggered, R4-D2, most likely triggered when the temps and rain level peaked during the overnight hours.  The avalanche appeared to include the majority of the ridge and was appoximately 300' wide and ran down slope up to 80' long.  Very large blocks and avalanche debris estimated to be 6' -8' deep.  High winds and poor visibility due to blowing snow prevented closer inspection or travel to higher elevations.

Photos:  Showing the avalanche debris on Wildflower Ridge, very poor visibility.  7800', north aspect, 35 degree slope.

Video #1:  Wildflower Ridge conditions at 7:30am.

Video#2:  ECTP-9 on windslab density change.  Video #2and #3 taken at N 39.30650, W 120.31757.  7932, 24 degree slope, north aspect.

Video#3:  PST 35/100 END on 12/2 facet layer

Avalanche Photos: 
Avalanche observation video: 

DonnerSummit2012 12 117 008

DonnerSummit2012 12 117 001

DonnerSummit2012 12 117 002

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

Raining up to 6400' at 6am and holding consistent through the mid morning.