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Loose Wet Avalanches Trigger Shallow Storm Slab

Location Name: 
Castle Lake
Region: 
Castle Lake
Date and time of avalanche (best estimate if unknown): 
Tue, 02/07/2017 - 1:00pm
Observation made by: 
Forecaster
Red Flags:
Recent avalanche activity
Recent loading by new snow, wind, or rain
Obvious avalanche path
Terrain Trap

Location Map

United States
41° 13' 27.5196" N, 122° 23' 22.1928" W
US

Avalanche Observations

Details

SS-NL-R2-D2

Multiple natural wet loose avalanches triggered a shallow storm slab avalanche on a north/northeast slope at 6000ft directly above Castle Lake.  The avalanche failed on a density break within the recent storm snow.  Yesterday's snow surface acted as smooth and relatively firm bed surface for the avalanche.  The wet and heavy 24hr snow failed as a soft slab 6 inches thick accross a 60ft section of the upper slope.  Multiple loose avalanches appeared to have initially triggered the shallow storm slab.  The avalanche entrained almost all of the 24hr storm snow on the entire path of the slide, creating an impressive debris pile that was 2-6ft deep.  The debris flow fractured the lake ice at the bottom of the slope and ripped branches off of a few trees.  The avalanche occurred this morning likely between 0500-1000 hours.

Several other wet loose avalanches ran this morning on the steep rocky slopes above Castle Lake.  No other storm slab avalanches were observed.  Several cornice fall avalanche were observed off of the ridgelines descending off of Middle Peak.  They all looked to have occurred during the recent storm events beginning last Thursday.  

Characteristics

Avalanche Type: 
WetSlabLoose/Point-Release
Trigger type: 
Natural
Slope: 
35degrees
Aspect: 
Northeast
Elevation: 
6 000ft.
Terrain: 
Near Treeline
Weak Layer: 
Storm Snow
Avalanche Width: 
80ft.
Avalanche Length: 
600ft.

Weather Observations

Details

Clearing skies throughout the day.  Winds were calm on Castle Lake and moderate to strong at ridgetop, blowing out of the southwest.  

Statistics

Cloud Cover: 
50% of the sky covered by clouds
Blowing Snow: 
Yes
Air temperature: 
Above Freezing
Air temperature trend: 
Warming
Wind Speed: 
Strong
Wind Direction: 
Southwest