Wind Slabs on Andesite Peak

Location Name: 
Andesite Peak
Region: 
Donner Summit Area
Date and time of avalanche (best estimate if unknown): 
Fri, 01/20/2017 - 15:45
Location Map: 
United States
39° 21' 2.7864" N, 120° 21' 56.2824" 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
Terrain Trap
Observation made by: Forecaster
Avalanche Observations
Avalanche Type: 
Dry
Slab
Slope: 
39degrees
Trigger type: 
Skier
Crown Height: 
2 ft
Aspect: 
Northeast
Weak Layer: 
Storm Snow
Avalanche Width: 
100ft.
Terrain: 
Above Treeline
Elevation: 
8 100ft.
Bed Surface: 
Storm Snow
Avalanche Length: 
200ft.
Number of similar avalanches: 
2
More detailed information about the avalanche: 

Small cornice pieces (microwave sized) dropped onto wind loaded slopes triggered wind slab avalanche 1.5 to 2.5 ft. deep. These wind slabs propagated across the slopes on a density change withing the storm snow. They were mostly D2 in size and involved enough snow to bury a person. Cornices were very fragile and could be triggered several feet away from the edges. Winds remained strong and wind loading continued to add snow to the wind slabs making them larger and more fragile into the afternoon and evening. Below treeline hand pits and tests showed instability on the same density change within the storm snow and ski kicks on below treeline sheltered slopes caused some cracking but no test slope failures. One ski cut on a steep below treeline slope did release a loose dry sluff.

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: 
Cooling
Wind Direction: 
Southwest
Accumulation rate: 
Greater than 1 in. per hour
More detailed information about the weather: 

Continued snow and strong winds throughout the afternoon.