Wet Loose Avalanches and Cornice Failures in Johnson Canyon

Location Name: 
Johnson Canyon
Region: 
Donner Summit Area
Observation Date & Time: 
Tuesday, April 11, 2023 - 11:30
Location: 
39.344616, -120.293604
Is this an Avalanche Observation?: 
Yes


Conditions Alerts:


Terrain Alerts: 
Terrain Matches the Advisory

Observation made by: Forecaster

Tabs

Observation
Description of Snow, Weather, and Avalanche Conditions: 

Driving up to Johnson Canyon today, I saw several new cornice collapses and wet loose avalanches on Donner Peak that must have happened yesterday afternoon. I could also see creeks flowing and water pouring out of the snow banks on the side of the road.

It was already soft and wet when I stepped onto the snow at Johnson Canyon. I sank into shin-deep wet snow even when standing in snowmobile tracks from yesterday. I continued up an S-facing ridge, where my skis sank several inches into wet snow at 11 am. 

Ski kicks above steep NE-E-SE facing test slopes off the ridge triggered ski width wide wet loose avalanches 3-4 inches deep between 11 am and noon. I also saw several cornice failures along this ridge that looked like they happened between yesterday afternoon and this morning. The cornice pieces that fell on the slope were big enough to crush a person. Water was streaming off the underside of the remaining cornices, and I could see cracks on the ridge behind the cornices. I did not approach these cornices and stayed on lower-angle slopes. The snow was wet and mushy everywhere I went during my tour. I departed the area at noon. 

Hide Terrain Details
Terrain: elevations: 
Near Treeline
Below Treeline
Terrain: aspects: 
NE
E
SE
S
Hide Avalanche Details
Avalanche Type: 
Wet Loose
Additional number of similar avalanches: 
5
Hide Trigger
Trigger: 
Skier
Trigger Modifier: 
Intentionally Triggered
Hide Terrain
Start Zone Slope Angle: 
35degrees
Aspect: 
Northeast
East
Southeast
Starting Elevation: 
near-treeline
Hide Size
Destructive Size: 
D1 Relatively harmless to people.
Relative Size: 
R1 Very Small
Crown Height: 
Less than 1 ft
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