Wind Slabs on Mt. Judah and Wildflower Ridge

Location Name: 
Mt. Judah
Region: 
Donner Summit Area
Date and time of avalanche (best estimate if unknown): 
Mon, 12/15/2014 - 13:00
Location Map: 
United States
39° 18' 1.2636" N, 120° 18' 57.7548" 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
Slope: 
39degrees
Trigger type: 
Natural
Crown Height: 
Less than 1 ft
Aspect: 
Northeast
Weak Layer: 
Storm Snow
Avalanche Width: 
200ft.
Terrain: 
Above Treeline
Elevation: 
8 120ft.
Bed Surface: 
Storm Snow
Avalanche Length: 
100ft.
Number of similar avalanches: 
3
More detailed information about the avalanche: 

More snow fell today than expected. By mid afternoon 5 to 6 inches of new snow existed above 7500 ft. in the Mt. Judah area. This new snow combined with S-SE winds to create small sensitive wind slabs on the ENE-NE-N aspects. The avalanche at the coordinates denoted in this observation occurred at 12:57pm when an oven-sized piece of cornice fell onto the wind loaded 38-39 degree (steepness) ENE (68 degrees in aspect) slope. This and the other avalanches seen today broke between 6 inches and 12 inches down on a layer of softer snow that fell at the onset of the precipitation. All of the wind slabs seen today quickly got thinner as one moved down slope and none of the avalanches ran down slope very far.

Photo 1: D1 avalanche on a 38-39 degree ENE aspect at 8120 ft. triggered by the natural cornice failure. This is the slide described above.

Photo 2: Skier-triggered D1 wind slab avalanche on Wildflower Ridge - a NE aspect, 38 to 40 degree slope, at ~7800 ft. - coordinates:39.307368, -120.318628

Photo 3: Shooting crack on a NNE facing test slope at ~8140 ft. Similar to other shooting cracks seen on wind loaded N-NE aspects.

Video: Small NE facing, 39-44 degree test slope on Wildflower Ridge adjacent to the slide in photo 2.

Avalanche Photos: 
Avalanche observation video: 

Wind Slab Failure on a Test Slope at Wildflower Ridge below Mt. Judah

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

5 to 6 inches of new snow had accumulated in this area by 2pm. This accumulation was about twice the amount expected. Wind transport of snow occurred all day and would fill in ski tracks with wind transported snow very quickly. Winds shifted between S and SE with a few bursts of SW winds. Most wind loading occurred on N-NE aspects with some wind loading on ENE-E aspects.