This avalanche was a combination of plenty of old settled powder that was available for the strong wind on Dec 12th to transport into fresh drifts. We also received about 5" of new snow on the 12th during the windy period. This bowl frequently avalanches when there is powder snow and wind to transport it.

This was on a mostly east facing slope, perhaps even a little southeast. There was very little old sugar snow near the ground on this aspect. The avalanche did not break into old sugar snow near the ground but rather in a layer higher in the snowpack, most likely the old snow surface from earlier this week. No mystery here, just a good shot of wind with plenty of powder snow to transport rapidly onto this slope until it couldn't hold anymore weight.

Looking at the opposite side of the ridge from the avalanche shows what happened. The slope that avalanched faces east. This slope faces west. It had about 2 feet of snow on it earlier this week which obviously got stripped by the wind and transported onto the east facing slope.