Wind Slabs, Cracking, and some Whumphing on Castle Peak

Location Name: 
Castle Peak
Donner Summit Area
Date and time of observation: 
Sun, 12/03/2017 - 13:00
Location Map: 
United States
39° 21' 55.2924" N, 120° 21' 28.3104" W

Red Flags: 
Whumphing noises, shooting cracks, or collapsing
Recent loading by new snow, wind, or rain

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

4 to 6 inches of new snow had accumulated since yesterday in the Castle Peak area. In most places, this new snow remained soft and unconsolidated. It existed on top of older weak sugary snow from before the storm (near surface facets). Tests and observations in sheltered areas did not reveal signs of instabilities at this interface in most areas; however, one party that we encountered did report triggering a whumph in the meadow near the Peter Grubb Hut. They said that the collapse was about 20 ft. in diameter, it wrapped around a corner, and the snowpack dropped about an inch. The weakness was "just below the new snow, but we didn't get a look at the snow grains."

In more wind-loaded areas, wind slabs had formed on leeward slopes and some fragile cornices existed above these slopes. The largest of the wind slabs we saw measured up to 24 inches in depth while most of them were 18 in. or less in depth.  Snowpit tests on wind-loaded test slopes yielded inconsistent results with some tests indicating that the wind slabs remained fragile and some tests showing the wind slabs starting to bond to the snowpack below them.  Ski cuts and kicks on wind-loaded test slopes also produced conflicting results. A ski kick on one N facing 40 degree test slope triggered a 25 ft. shooting crack that wrapped around a corner similar to those seen by an avalanche class on Andesite Ridge (photo), but ski cuts and kicks on other slopes did not produce cracking. 

Snowpit or crown profile photo or graph: 
Weather Observations
Blowing Snow: 
Cloud Cover: 
25% of the sky covered by clouds
Air temperature: 
Below Freezing
Wind Speed: 
Air temperature trend: