Wet slab avalanches on Donner Summit.

Location Name: 
Andesite Ridge
Region: 
Donner Summit Area
Date and time of avalanche (best estimate if unknown): 
Tue, 02/07/2017 - 08:30
Location Map: 
United States
39° 20' 29.8968" N, 120° 21' 13.1688" W
See map: Google Maps
US


Red Flags: 
Recent avalanche activity
Recent loading by new snow, wind, or rain
Obvious avalanche path
Observation made by: Forecaster
Avalanche Observations
Avalanche Type: 
Wet
Slab
Trigger type: 
Natural
Crown Height: 
Less than 1 ft
Aspect: 
East
Weak Layer: 
Storm Snow
Avalanche Width: 
100ft.
Terrain: 
Near Treeline
Elevation: 
7 580ft.
Bed Surface: 
Storm Snow
Avalanche Length: 
30ft.
Number of similar avalanches: 
More than 10
More detailed information about the avalanche: 

New wet slab avalanches from this morning and older wet slab avalanches from sometime late yesterday or last night were widespread on Andesite Ridge and in the greater Donner Summit area. Numerous avalanche crowns were visible from I-80 on both the N and S sides of the Hwy on N-NE-E-SE aspects. These were in addition to the photos in this observation taken on Andesite Ridge. Crown profiles at the avalanches on Andesite Ridge revealed that the snowpack was failing at the interface between wet rain soaked surface snow and dry recent storm snow below. Avalanches seen were all size D1 to D2 and occurred on slopes steeper then 35 degrees. Fairly wide propagation relative to the overall size of the avalanche was noted in some areas.

Rain runnels on the snow surface were widespread on all aspects. Numerous areas of standing and running water were noted on roadways at I-80 pass level (7,227')

Avalanche Photos: 
Weather Observations
Cloud Cover: 
100% of the sky covered by clouds
Air temperature: 
Above Freezing
Wind Speed: 
Strong
Precipitation: 
Rain
Air temperature trend: 
Static
Wind Direction: 
Southwest