Avalanches Failing on Surface Hoar in Deep Creek

Location Name: 
Deep Creek
Region: 
Cabin Creek, Deep Creek, or Pole Creek Area
Date and time of avalanche (best estimate if unknown): 
Sun, 12/13/2015 - 11:00
Location Map: 
United States
39° 14' 47.3748" N, 120° 14' 3.354" 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
Obvious avalanche path
Observation made by: Forecaster
Avalanche Observations
Avalanche Type: 
Dry
Slab
Slope: 
37degrees
Trigger type: 
Natural
Crown Height: 
1 ft
Aspect: 
North
Weak Layer: 
Other
Avalanche Width: 
300ft.
Terrain: 
Near Treeline
Elevation: 
7 700ft.
Bed Surface: 
Other - explain below
Avalanche Length: 
75ft.
Number of similar avalanches: 
2
More detailed information about the avalanche: 

Approximately 25-30cm of new snow in the Deep Creek area by mid afternoon above 7500'.  This storm came in wet with a crust forming at the new snow/old snow interface up to at least 7800'.  In many areas this new snow was able to bury a layer of surface hoar that was preserved in places that were protected from the warm temps and winds from yesterday.  This surface hoar layer was mostly easy to identify with hand pits throughout our tour and was reactive in all snowpack tests.  We found the surface hoar layer on N-NE aspects, near and below treeline, in open areas.  In some places the surface hoar was not found and thought to be destroyed or was observed to be layed over and not posing as great of an instability.

Natural avalanche that appeared to be cornice triggered.  38 degree wind loaded slope, N-NE aspect, 7700', 8-12'' slab, 300' wide x 75' downslope.  Photo #1 and #2.

Skier triggered avalanche from a party of skiers in front of us.  37 degree slope, N aspect, 7680', 8-12'' slab, 75' wide x 100' downslope.  Photo #3.

 

 
 

Avalanche Photos: 
Weather Observations
Blowing Snow: 
Yes
Cloud Cover: 
100% of the sky covered by clouds
Air temperature: 
Below Freezing
Wind Speed: 
Moderate
Precipitation: 
Snow
Air temperature trend: 
Cooling
Wind Direction: 
Southwest
Accumulation rate: 
Greater than 1 in. per hour