Slough avalanche in 3-D chute

AVALANCHE OBSERVATION
3-D Chute behind June Mtn,

Drainage:

Submission Info
josh feinberg
Forecaster
Monday, December 16, 2019 - 1:00pm
Avalanche Type: 
Loose/Point-Release
Trigger type: 
Skier
Aspect: 
Northeast
Weak Layer: 
Storm Snow
Terrain: 
Near Treeline
Elevation: 
10 500ft.
Bed Surface: 
Storm Snow
Number of partial burials: 
0
Number of full burials: 
0
More detailed information about the avalanche: 

 

A party of 3 (2 snowboarders and 1 skier) rapelled into 3-D chute behind june Mtn after riding a line in the negatives previously that day.  Mid-way down the skier (descending 2nd after a snowboarder) triggered some loose sloughing and ended up turning into the slough causing him to lose control, crash and blow out his knee.  The party splinted the injured skiers knee and was able to self-extricate doing 5 rappels, and then work their way slowly back towards the ski area.  The June Mtn ski patrol met them before making it back into the boundary and was able to evacuate the skier to medical attention.  

The avalanche advisory that day was MODERATE for treeline and above for fresh wind slabs, and the final line in the discussion cautioned of loose sloughs in steep terrain. "Extreme terrain features such as steep couloirs and rolling convexities may present the most hazard for wind slab instabilities or loose snow sloughing right now."

5" of new snow was recorded at Mammoth Mtn (9000') falling the night of Dec 13th. Cold temperatures persisted and winds continued to transport loose snow for several days after this.    

ESAC forecaster made field observations that same day in the Negatives and the Hemlocks, and reported specifically about the negatives: "No signs of cracking or instability other than some manageable moderate sloughing."

This accident was caught on video, see attached.  

Avalanche observation video: 
More detailed information about the weather: 

12:30pm, 11,100' air temp = -10°C.

Winds resulted in some transport in the morning, but afternoon winds decreased and transport stopped.  

Number of People Caught: 
1
37° 44' 6.3312" N, 119° 5' 42.378" W
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