Wind Slabs on Mt. Rose

Location Name: 
East Ridge Tamarack Peak
Region: 
Mount Rose Area
Date and time of avalanche (best estimate if unknown): 
Fri, 04/13/2012 - 11:00
Location Map: 
United States
39° 18' 45.5796" N, 119° 54' 40.2012" 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: Professional Observer
Avalanche Observations
Avalanche Type: 
dry,slab,
More detailed information about the avalanche: 

Around 12'' of new snow in the Mt. Rose area with just over 2' in wind loaded terrain.  In protected non wind loaded terrain there were no signs of instabilities today.  Several ECT's in these more protected areas showed no propagation.  In wind loaded exposed terrain there were well formed wind slabs that were very reactive to large cornice drops.  There were 2 natural avalanches that occured sometime in the early morning and were mostly covered up with new snow-thought to be caused by natural cornice failure.

Cornices were very fragile and built out.  They failed easy with a ski kick and large fridge size blocks caused failure of the wind slab below.  Most of these wind slabs were 2' deep and failing 2-3'' above the old snow/new snow interface on a storm snow weakness.  Some of these wind slabs were in the D2 range. 

By the early afternoon, the wind slab has gained some strength.  Large cornice drops were not causing as much propagation and slabs were not running as far.  Additional loading, snow and wind, had pretty much ended by noon.

Photo #1:  9300', N aspect, 35-40 degree slope, wind slab failure caused by intentional cornice drop.

Photo#2:  Debris running full path.

Photo #3: 9700', N aspect, 35-40 degrees, just east of Prolitariate Bowl.  Less slab propagation in this area

Photo #4:  Looking back at East Ridge 9300' showing some of the wind slab activity with some better visibility.

Video:  Weather conditions at 10am at 9300' on the East Ridge and showing wind slab failure.

Avalanche Photos: 
Avalanche observation video: 

MtRose2012 4 13 008

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: 
Warming
Wind Direction: 
Southwest
Accumulation rate: 
Less than 1 in. per hour
More detailed information about the weather: 

S-2 snow in the morning hours tapering off by midday with some sun peaking through the clouds.  Moderate SW winds shifting by noon towards NW and decreasing in speed.