Skier triggered collapses and buried surface hoar on Donner Peak.

Location Name: 
Donner Peak
Region: 
Donner Summit Area
Date and time of observation: 
Sat, 01/16/2016 - 11:25
Location Map: 
United States
39° 18' 35.6652" N, 120° 19' 3.8208" 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
Observation made by: Forecaster
Snowpit Observations
More detailed information about the snowpack: 

A total of three, fairly isolated skier triggered collapses were observed in this area today. All occurred in open areas below treeline on low angle to flat sections of a macro scale N to NE aspect in the 7,600' to 7,700' range. Snowpack collapse seemed to radiate up to 20 feet away from the trigger point, so propagation potential was obvious. Two of the three collapses occurred in areas with previous skier traffic. A testpit dug adjacent to the area of two of the collapses in an area previously traveled by numerous skiers yielded CTM-12 sudden collapse results on 6 to 10 mm surface hoar buried 75 cm below the snow surface.

Photo 1: Buried surface hoar layer at the CTM-12 sudden collapse failure layer interface.

Photo 2: Testpit showing the depth at which the buried surface hoar layer failed, 75 cm below the snow surface. Probe is in back right corner of failure plane.
 

Snowpit or crown profile photo or graph: 
Snowpack photos: 
Weather Observations
Blowing Snow: 
No
Cloud Cover: 
100% of the sky covered by clouds
Air temperature: 
Above Freezing
Wind Speed: 
Light
Precipitation: 
Rain
Air temperature trend: 
Static
Wind Direction: 
Southwest
More detailed information about the weather: 

Rain was observed in this area at the high point of travel around 7,800'. Rain may have been occurring in this area as high as 8,200'.