Loose dry sluffs, shooting cracks, and fragile cornices on Silver Peak

Location Name: 
Silver Peak
Region: 
Cabin Creek, Deep Creek, or Pole Creek Area
Date and time of observation: 
Fri, 04/13/2012 - 14:00
Location Map: 
United States
39° 13' 32.7756" N, 120° 14' 18.8916" 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
Terrain Trap
Observation made by: Forecaster
Snowpit Observations
More detailed information about the snowpack: 

16 inches of recent snow existed on top of a thick melt-freeze crust. In wind loaded areas snow since Wednesday measured about 3 ft deep. Several weaknesses existed in the recent snow: at the base of the new snow a thin layer of less dense snow existed just above the crust. Above this a more dense layer of snow existed and lighter snow rested on top of that. The more dense layer of snow was much thicker in the wind loaded areas than in non-wind affected areas. Early in the day skier triggered shooting cracks and some slab failures did occur on steep wind affected test slopes. By the afternoon only shooting cracks and no slab failures occurred on similar test slopes. Snowpit data showed that fracture could still occur as the weaknesses within the storm snow broke but that those fractures would not travel very far.

Ski cuts on steep test slopes triggered loose dry snow sluffs involving the top 8-12 inches throughout the day in both above and below treeline. Cornices dropped on wind-loaded slopes in near and above treeline terrain also produced loose snow sluffs but did not trigger any slab failures.

Photo 1: Shooting crack and slab failure on the edge of a loose snow sluff on a steep wind loaded below treeline test slope.

Photo 2 and 3: Skier triggered loose snow sluffs in below treeline terrain

Photo 4: Cornice triggered sluff in near treeline terrain.

Snowpack photos: 
Weather Observations
Blowing Snow: 
No
Cloud Cover: 
100% of the sky covered by clouds
Air temperature: 
Below Freezing
Wind Speed: 
Calm
Precipitation: 
None
Air temperature trend: 
Warming
Wind Direction: 
Accumulation rate: 
More detailed information about the weather: 

Calm winds and cool temperatures prevailed throughout the day. Occasionally breaks of sun would poke through the clouds. On those slopes that did receive sun, it quickly started to warm the snow surface and make it heavier. In some areas enough melting may have occurred for a sun crust to form on some slopes.