Wind Slabs on Castle Peak

Location Name: 
Castle Peak
Region: 
Donner Summit Area
Date and time of observation: 
Wed, 12/20/2017 - 12:00
Location Map: 
United States
39° 21' 36.7812" N, 120° 21' 49.4748" W
See map: Google Maps
US


Red Flags: 
Observation made by: Forecaster
Snowpit Observations
More detailed information about the snowpack: 

About 4 inches of new snow had accumulated in the Castle Peak area since yesterday. Precipitation in this are had stopped, and the storm had cleared out before we started our tour at 10 am. In sheltered areas where the old snow surface had been weak and unconsolidated (near surface facets), the new snow did not have enough slab characteristics to pose a problem. In more exposed areas where wind-loading had occurred, wind slabs had formed. These wind slabs ranged from 6 to 14 inches and depth and existed in areas near ridgelines. Ski kicks on wind-loaded NE-E test slopes steeper than 38 degrees did trigger shooting cracks and one test slope failure. These wind slabs failed on the interface between the new wind slab and old crusts at the base of the wind slab. Later in the afternoon, snowpit tests on less steep, less wind-loaded, NW aspects where previous hard slabs existed yielded inconsistent results (ECTN, ECTN, PST 95/100, PST 57/100).

Photo 1: Shooting cracks triggered by ski kicks on an E facing wind-loaded test slope at 7900 ft.

Photo 2: The same slope after it failed on the next ski kick. 

Snowpack photos: 
Weather Observations
Blowing Snow: 
No
Cloud Cover: 
25% of the sky covered by clouds
Air temperature: 
Below Freezing
Wind Speed: 
Light
Precipitation: 
None
Air temperature trend: 
Static
Wind Direction: 
Northwest
Accumulation rate: 
More detailed information about the weather: 

The sudden end to the storm brought light winds and sunny skies to the area before 10 am.