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Natural Wind Slab Avalanche

Location Name: 
Avalanche Gulch
Region: 
Mt. Shasta
Date and time of avalanche (best estimate if unknown): 
Fri, 12/27/2019 - 11:30am
Observation made by: 
Forecaster
Red Flags: 
Recent avalanche activityWhumphing noises, shooting cracks, or collapsingRecent loading by new snow, wind, or rain

Location Map

96067 Mount Shasta , CA
United States
41° 22' 8.4612" N, 122° 13' 18.1308" W
California US

Avalanche Observations

Details

This natural trigger, wind slab avalanche was witnessed and observed at 1130 hours on 12.27.19. It occurred near treeline on a W/NW facing aspect off Green Butte Ridge/Broadway and slid into Avalanche Gulch through sparse trees. Avalanche size of D1.5. This avalanche was relatively small but big enough to potentially bury someone in a terrain trap and certainly big enough to sweep someone off their feet into undesirable terrain such as trees in this case. Estimated crown height was 18 inches tall and 100 feet wide. It is our best guess at this point that the avalanche failed on the 12/19 ice crust.

A strong, northwest wind event was very productive in moving a ton of snow around (visible in photos). Leeward aspects were actively being wind loaded and some slopes, like this one, cross-loaded. Exposed ridgelines and other windy terrain were completely stripped of the previous 6-12 inches of low density snow. This has left behind the 12/19 ice crust.

Photos

Characteristics

Avalanche Type: 
Slab
Trigger type: 
Natural
Slope: 
37degrees
Aspect: 
Northwest
Elevation: 
8 200ft.
Terrain: 
Near Treeline
Weak Layer: 
Old Snow
Bed Surface: 
Other - explain below
Crown Height: 
2 ft
Avalanche Width: 
100ft.
Avalanche Length: 
500ft.
Number of people caught: 
0
Number of partial burials: 
0
Number of full burials: 
0

Weather Observations

Details

Statistics

Cloud Cover: 
Clear
Blowing Snow: 
Yes
Precipitation: 
None
Accumulation rate: 
None
Air temperature: 
Below Freezing
Air temperature trend: 
Warming
Wind Speed: 
Gale Force
Wind Direction: 
Northwest