Wet Snow and Melting Cornices in Johnson Canyon

Location Name: 
Johnson Canyon
Region: 
Donner Summit Area
Observation Date & Time: 
Saturday, April 29, 2023 - 11:00
Location: 
39.345402, -120.294259
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: 

I went to Johnson Canyon hoping to take advantage of last night's slight inversion. The cooler temperatures at lower elevations did allow for a slightly better refreeze, but as soon as I climbed above 7000 ft, I started sinking into ankle-deep wet snow on E and SE aspects at 9:45 am. Ski cuts on NE-E-SE facing test slopes triggered small D1 wet loose avalanches by 10:00 am. I found the most supportable snow on the ridge where the winter winds left more dense snow. I also found large cornices along the ridge. Many of these had already collapsed. Now they are melting and slumping onto the slopes below. As they pull away from the ridge, they leave large crevasse-like cracks behind. I descended on low-angle S-SW-W aspects, hoping the refreeze had not melted entirely. By the time I got down around 11:30, ankle-deep wet snow also existed on these slopes. 

Hide Avalanche Details
Avalanche Type: 
Wet Loose
Additional number of similar avalanches: 
3
Hide Trigger
Trigger: 
Skier
Trigger Modifier: 
Intentionally Triggered
Hide Terrain
Start Zone Slope Angle: 
35degrees
Aspect: 
Northeast
East
Southeast
South
Southwest
Starting Elevation: 
below-treeline
near-treeline
Hide Size
Destructive Size: 
D1 Relatively harmless to people.
Relative Size: 
R1 Very Small
Crown Height: 
Less than 1 ft
Avalanche Width (Average width): 
30ft.
Avalanche Length (Vertical Run): 
30ft.
Hide Weather Details
Elevation of Observation: 
6000-7000 ft.
7000 - 8000 ft.
Wind Direction: 
Southwest
Wind Speed: 
Moderate
Sky Cover: 
Few - Mostly Clear - up to 2/8 covered
Air temperature: 
Above Freezing
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