Intense blowing and natural wind slab avalanches on Flower Ridge.

Location Name: 
Flower Ridge, Mt. Judah
Region: 
Donner Summit Area
Observation Date & Time: 
Friday, December 24, 2021 - 10:30
Location: 
39.308009, -120.319523
  • MapBuilder Topo
  • MapBuilder Hybrid
  • Forest Service 2016
  • NAIP 2013
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Is this an Avalanche Observation?: 
Yes


Conditions Alerts:


Terrain Alerts: 
Slopes Steeper than 30 degrees
Obvious Slide Path
Trigger Points
Terrain Matches the Advisory

Observation made by: Public

Tabs

Observation
Description of Snow, Weather, and Avalanche Conditions: 

We went to Flower Ridge and the north end of the Mt. Judah summit today to look at wind loaded slopes and to be able to easily avoid avalanche terrain. We were able to find our first wind loaded test slope just a few feet from the parking lot and were quickly able to determine that cornices would collapse very easily today.

Moving up towards the ridgetop through sparsely treed terrain we were able to utilize numerous wind loaded test slopes to gather wind slab info. We found 4F+ hard wind slabs 8 to 12 inches thick sitting on top of F hard storm snow. Most of the time when we collapsed the corniced test slopes, the cornice chunks just entrained snow. In only a couple of instances did we propagate a wind slab failure on the test slopes.

As we came to Flower Ridge, blowing snow was intense. In the slight visibility breaks between max wind gusts we were able to see two natural wind slab avalanches with one foot crowns. The first one had happened prior to our arrival. The second occurred while we were on the ridgetop viewing the first. Both were triggered by natural cornice collapse.

We encountered one open creek at around 7,200' that still had an impressive amount of flowing water following the Dec 22 rain event.

Ridgetop travel was slightly difficult while travel in below treeline non-avalanche terrain was fairly easy due to the density of the new snow and only about 6 inches of ski penetration.

Snowpack, Avalanche, Weather Videos: 

Flower Ridge blowing snow and natural wind slab avalanches.

Hide Avalanche Details
Avalanche Type: 
Wind Slab
Failure Plane/Weak Layer: 
Storm Snow
Additional number of similar avalanches: 
2
Hide Trigger
Trigger: 
Natural
Trigger Modifier: 
Cornice Fall Triggered
Hide Terrain
Aspect: 
Northeast
Starting Elevation: 
near-treeline
Hide Size
Destructive Size: 
D2 Could bury, injure, or kill a person.
Relative Size: 
R2 Small
Crown Height: 
1 ft
Avalanche Width (Average width): 
50ft.
Avalanche Length (Vertical Run): 
75ft.
Hide Weather Details
Elevation of Observation: 
7000 - 8000 ft.
8000 - 9000 ft.
Blowing Snow: 
Intense
Wind Direction: 
Southwest
Wind Speed: 
Gale Force
Sky Cover: 
Overcast - Cloudy - 8/8 covered
Highest Precipitation Rate: 
Light Snowfall (S1 (S-1 = 1 cm /~.5 in per hour)
Precipitation: 
Snow
Air temperature: 
Below Freezing
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