Triggered with a cornice drop. 

"A first cornice stomp entrained a sizeable sluff, and then a
secondary cornice drop trigger a fast, powerful slide that propagated over
ridgelines and blasted all the way down to the apron (1,000' vertical
feet?).  It packed a big punch and would have been bad news to have been
caught in.  
Most of the slab was a result of wind loading in the new snow, which had
bonded to the previous 6" and then all slid on the ice layer.

The slabs are kind of sticky - they hang in place, but when they cut
loose, they are fast.  In terrain like this (wind loaded, steep, upper
elevation, northish facing) I think the danger is pushing "considerable.""