Natural deep slab avalanche on Donner Summit

Location Name: 
St. Paddy's Bowl
Region: 
Donner Summit Area
Date and time of avalanche (best estimate if unknown): 
Sat, 03/17/2012 - 02:00
Location Map: 
United States
39° 18' 17.4564" N, 120° 21' 40.1292" W
See map: Google Maps
US


Red Flags: 
Recent loading by new snow, wind, or rain
Obvious avalanche path
Observation made by: Forecaster
Avalanche Observations
Avalanche Type: 
dry,slab,
Slope: 
40degrees
Trigger type: 
Natural
Crown Height: 
8 ft
Aspect: 
North
Weak Layer: 
Old Snow
Avalanche Width: 
1 200ft.
Terrain: 
Below Treeline
Elevation: 
7 150ft.
Bed Surface: 
Old Snow
Avalanche Length: 
350ft.
More detailed information about the avalanche: 

This is another deep slab natural avalanche that occurred at the very tail end of snowfall during the very early morning hours (circa 2am) of March 17.

Noted lat/long is very approximate and could be slightly incorrect, but the general location west and outside of the Sugar Bowl Ski Area boundary is correct.

Photo's 1-3 looking up the avalanche, crown is barely visible in the photos.

Photo 4 - Looking down the avalanche at the debris.

Below are edited excerpts from the report supplied by the party who came across the evidence of the this avalanche around 4:30 pm on March 17.

"Best description of the location is if you descend west from Crow's Nest on the ridge towards Rowton/Serene Lakes, the ridge levels off just after crossing the top point of a slight gully/drainage.  At that point, dropping to the north (towards Old 40/same aspect as Strawberry Fields) there is a meadow that rolls over below treeline into a steep open bowl. The bowl itself as it is at least 35+ degrees to 45 degrees. It gets wind loading out of the meadow above.
 
Didn't go too close to inspect, but our guess from looking at it from below, was the fracture was probably 400 yds across or the entirety of the bowl, crown was from 5 to 8 feet, and the staunch wall (at least on the skiers' right that we could see) was also of similar depth.  It ran approx. 350 vt. feet, and well through the trees and across a bench.  Didn't inspect the bed surface. 
 
Further to the skiers' right (and on a slight ridge up from the other side of a gully) about 120 yards to the right of the staunch wall, there were sympathetic cracks on the snow surface. Guess is that the slide ran either late Friday night or early Sat. morning as there was a slight dusting of snow on the debris, and this was before it started to snow again late afternoon/early evening on the 17th.
 
We were out there at about 4:30 p.m., and experienced no collapsing, whumpfing, cracks or sloughing. Didn't measure the depth of the debris."
Avalanche Photos: 
Weather Observations
Air temperature: 
Precipitation: 
Air temperature trend: 
Wind Direction: 
Accumulation rate: 
More detailed information about the weather: