Wind loading from SW winds created moderately sized cornices and deposited higher density snow ontop of low density storm snow. The rapid loading and possible cornice failure most likely caused the intial failure. This intial soft slab failure then stepped down onto the old faceted snow below the surrounding rock bands aiding in propegation across a wider area of the slope. With the debris and crowns being somewhat obscured by new snow, I would venture to guess that this occurred earlier into the storm than the avalanches on Cascade.