Wet Snow and Large Cornices in Negro Canyon

Location Name: 
Negro Canyon
Region: 
Donner Summit Area
Date and time of observation: 
Sat, 02/18/2017 - 13:00
Location Map: 
United States
39° 20' 59.388" N, 120° 18' 6.2316" W
See map: Google Maps
US


Red Flags: 
Whumphing noises, shooting cracks, or collapsing
Recent loading by new snow, wind, or rain
Rapid warming
Obvious avalanche path
Observation made by: Forecaster
Snowpit Observations
More detailed information about the snowpack: 

Warm air and cloud cover with light rain below 6600 ft. and wet snow above 6600 ft. caused a heavy wet layer of snow about 4 to 5 inches thick to form on the snow surface on all aspects in this area today. Ski cuts on steep test slopes resulted in ski-width, loose, wet sluffs. Near ridgelines, the strong SW winds were transporting snow and building wind slabs and cornices on the leeward aspects. Ski kicks would easily trigger cornice failures but those pieces of cornice only triggered wet sluffs in that involved the wet snow on all but one test slope. One N facing test slope did have cracks that propagated about 1 ft. wider than the cornice pieces in the wind slab below the cornice.  

Photo 1: Ski cut triggered loose wet sluff on a NE facing test slope.

Photo 2: Small wind slab triggered by dropping a cornice onto a N facing test slope.

Photo 3: Ski kick triggered loose wet sluffs on an E facing test slope.

Snowpack photos: 
Weather Observations
Blowing Snow: 
Yes
Cloud Cover: 
100% of the sky covered by clouds
Air temperature: 
Above Freezing
Wind Speed: 
Strong
Precipitation: 
Mixed rain and snow
Air temperature trend: 
Warming
Wind Direction: 
Southwest
Accumulation rate: 
Less than 1 in. per hour
More detailed information about the weather: 

Rain below 6600 ft and wet heavy snow above. Strong SW winds.