Wind Slab Cracking Near Drifter Bowl

Location Name: 
Drifter Bowl
Region: 
Donner Summit Area
Date and time of observation: 
Fri, 12/25/2015 - 12:45
Location Map: 
United States
39° 21' 6.5088" N, 120° 17' 14.7048" W
See map: Google Maps
US


Red Flags: 
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 ridge between Drifter Bowl and Sunrise Bowl, ski cuts on wind loaded test slopes triggered cracks that shot 10 ft from the ski tips. On the steeper wind loaded test slopes some small wind slabs failed as a result of ski cuts. These measured up to 18 inches in depth and did not travel very far down hill since the slopes that were tested were only 5 to 10 ft tall.

Cornices remained fragile above these test slopes and would break several feet back from the edge under the weight of a skier. Some of the cornice pieces would trigger cracking in the wind loaded slopes below and others did not. On many of these test slopes evidence that they broke during the storm existed and was now partially buried under new snow. Large cornices existed above Drifter Bowl. No active wind loading was occurring in this area today.

Snowpit data and probing in near and below treeline terrain did not show any signs of the 12/13 rain crust or the previously buried surface hoar. Some tests did indicate that a facet layer may be forming under the 12/24 rain crust which is currently about 5 inches thick and very strong in this area (ECTP 22, ECTN 21, 2m ECTN 24 all just below the 12/24 rain crust). Snowpit data and observations also indicated that the new snow is starting to consolidate and bond to the crust below it.

Photos 1 and 2: Skier triggered cracking on N-NE facing wind loaded test slopes. 

Photo 3: A skier triggered cornice collapse that propagated about 20 ft from my ski tips. 

Snowpack photos: 
Weather Observations
Blowing Snow: 
No
Cloud Cover: 
50% of the sky covered by clouds
Air temperature: 
Below Freezing
Wind Speed: 
Light
Precipitation: 
Snow
Air temperature trend: 
Static
Wind Direction: 
North
Accumulation rate: 
Less than 1 in. per hour
More detailed information about the weather: 

Winds started to shift to the north around 1:30 pm but still remained light. Some small scattered snow showers moved through the area between 10 am and 2 pm but did not produce enough snow for measurable accumulation.