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Cornice Triggered slide on The Playground

Location Name
The Playground
Region
Tam Rim Area
Name
Adam Craig
Email Address
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Position
Public
Date and time of avalanche (best estimate if unknown)
Red Flags
Recent loading by new snow, wind, or rain
Obvious avalanche path
Avalanche Type
Slab
Blowing Snow
Yes
Trigger type
Other-please explain in the comments
Wind Speed
Moderate
Slope
40degrees
Wind Direction
West
Air temperature
Below Freezing
Aspect
Northeast
Air temperature trend
Cooling
Bed Surface
Storm Snow
Cloud Cover
75% of the sky covered by clouds
Precipitation
Snow
Weak Layer
Storm Snow
Crown Height
3 ft
Accumulation rate
<1
Avalanche Width
400ft.
Avalanche Length
800ft.
Terrain
Near Treeline
More detailed information about the weather

 Typical Tam Rim day, breaks of sun, times of heavy cold snow, big flakes, small flakes.  Lots of wind transport.  

More detailed information about the avalanche

 We initially cut some small cornice chunks onto this slope on the West end of the playground area at Tam Rim with a G3 cable.  These chunks were small and soft but sluffed the slope and we planned to ski a different run then return here to ski later.  Upon return, we had met up with Shane of Three Sisters Backcountry who had a proper rope in his pack for a proper cut.  We dropped a human sized chunk of old cornice and the whole slope slowly broke, propagated right and left at the crown, ran over some cliffs then propagated faaaar left in the bowl below.  The debris ran into the flats and was about 1.5m deep.  Another cornice was dropped where the aspect changed 20 degrees or so north, skiers right of the crown, and no activity was prompted on this concave, well supported slope with limited trigger points.  We skiied this slope into the debris pile to check out the lower crown, which had broken to the same mid-storm snow mystery layer and was about 3' tall.  Shane was belayed down to the crown, about 5' below the cornice, and did a crown profile.  He found the bed surface 6" above the old january rain crust amidst the new storm snow.  With my low powered glass he was unable to distinguish any persistent weak layer and determined that the weak layer was simply a mystery mid-storm layer from a small temperature shift or wind shift during the storm or a lull.  The snow structure was Fine and he was able to get Q3 shear results at the crown.  He also reported being able to detect a change in density at the bed surface from a solid 4-finger penetration to a softer full fist penetration, but, again, no change in the grain structure.  Shane is the one who was in there so more direct questions can be directed his way.  He's usually on a snowmobile somewhere between three creeks snow park and the lake...