Hard Wind Slabs, Scoured Surfaces, and Soft Snow on Castle and Basin

Location Name: 
Castle Peak and Basin Peak
Region: 
Donner Summit Area
Date and time of observation: 
Tue, 12/05/2017 - 12:00
Location Map: 
United States
39° 23' 1.4568" N, 120° 21' 56.196" W
See map: Google Maps
US


Red Flags: 
Recent loading by new snow, wind, or rain
Observation made by: Forecaster
Snowpit Observations
More detailed information about the snowpack: 

In near and below treeline areas sheltered from the NE winds, 2 to 4 inches of soft, unconsolidated, recent storm snow remained on the surface. Below this surface snow, a layer of older looser weaker snow existed. These soft surface layers rested on top of a firm and supportable rain crust. In these sheltered areas, hand pits, ski cuts on test slopes, and general observations did not reveal any signs of instability. 

In areas exposed to the NE winds, variable surfaces existed ranging from firm icy scoured surfaces to wind packed snow to areas where a mix of scoured surfaces and some remaining soft snow existed. Most of the scouring took place on exposed N-NE-E aspects in near and above treeline terrain or along ridgelines, but some of the more exposed and open N-NE-E aspects below treeline also exhibited signs of wind scouring.

The strong E and NE winds had redeposited snow onto the NW-W-SW-S aspects along the ridgelines of Castle and Basin Peak. These new wind slabs were hard and stubborn to trigger, but tests on these hard slabs yielded unstable results that indicated the right trigger in the right place could cause them to break away from the weaker snow below them (ECTPV and 2m ECTP 10 failing on the weaker old snow below the wind slab and above the rain crust). These new wind slabs were limited to specific wind-loaded slopes near ridgelines in near and above treeline terrain. The NE winds continued to transport snow throughout the day. 

Photo 1: Scoured surfaces on a N aspect on Basin Peak @ 8800 ft.

Photo 2: Softer unconsolidated snow on a below treeline N aspect sheltered from the NE winds @ 8200 ft. above Devils Oven Lake.  

Video: 2m ECTP 10 failing on the weaker old snow above the rain crust and below the hard wind slab on a cross-loaded NW aspect on Castle Peak. While it may be difficult to trigger these hard wind slabs, these tests show that if they do break, the fractures can travel through the weak layer.  Coordinates: 39.36496, -120.35857.

Snowpack photos: 
Snowpit videos (tests, etc): 

2m ECTP on a cross-loaded NW aspect on Castle Peak

Weather Observations
Blowing Snow: 
Yes
Cloud Cover: 
Clear
Air temperature: 
Below Freezing
Wind Speed: 
Strong
Air temperature trend: 
Warming
Wind Direction: 
Northeast
More detailed information about the weather: 

Blowing snow along the ridgelines all day.