Wind Slabs on Castle Peak

Location Name: 
North Side of Castle
Region: 
Donner Summit Area
Date and time of observation: 
Wed, 12/17/2014 - 11:30
Location Map: 
United States
39° 21' 46.6452" N, 120° 20' 26.124" W
See map: Google Maps
US


Red Flags: 
Recent avalanche activity
Whumphing noises, shooting cracks, or collapsing
Recent loading by new snow, wind, or rain
Obvious avalanche path
Observation made by: Forecaster
Snowpit Observations
More detailed information about the snowpack: 

On the way up to the north bowl, ski cuts on wind loaded N-NE-E tests slopes in near and above treeline terrain resulted in shooting cracks up to 8ft. in length that failed on a layer of softer snow near the base of the wind slabs or on a sun crust at the base of the wind slab. On one E facing test slope at 7960 ft, one step on the slope triggered a crack and the next step released a 12 to 16 inch deep wind slab that slid on top of a sun crust. Some near crust facets may exist on top of the crust. An oven sized piece of cornice dropped on a larger E-NE facing test slope near by triggered a small wind slab avalanche with a 6 to 8 inch crown. In the north bowl large cornices existed above most NE-N aspects. On small test slopes between 8200 and 8400 ft. small cornice pieces dropped onto wind loaded N-NE test slopes also triggered cracking with the layer of softer snow serving as the weak layer. No sun crusts existed on the N-NE aspects. Snowpit tests through out the day indicated that the wind slabs could fail and that fractures could propagate along whatever weak layer was below them. Tests in non-wind loaded areas indicated that fracture propagation was unlikely.

Photo 1: Shooting crack triggered by one step on the the E facing test slope at 39.35594, -120.34091

Photo 2: The wind slab on that slope moving down slope after the next step.

Photo 3: Snow grains on top of the crust that the slab above failed on. It looks like some near crust facets have started to form (red arrow points to one such grain).

Photo 4: Small wind slab avalanche triggered by an oven sized piece of cornice dropped onto the slope.

 

Snowpack photos: 
Weather Observations
Blowing Snow: 
Yes
Cloud Cover: 
100% of the sky covered by clouds
Air temperature: 
Below Freezing
Wind Speed: 
Moderate
Precipitation: 
Snow
Air temperature trend: 
Cooling
Wind Direction: 
Southwest
Accumulation rate: 
Less than 1 in. per hour
More detailed information about the weather: 

2 to 3 inches of new snow in this area at the start of the tour. During the tour another 1 to 3 inches fell. Snowfall rates up to 1 in/hr were observed.