Updated information:
Note that there was no wind effect of wind loading on the slope. This slab in Goldpan was triggered without any red flags prior and caught the group by surprise. There is a buried layer of surface hoar around a foot deep that formed on top of the Nov 9 storm and under the snow that has trickled in over the past week. It has been hard to find in places, but present in others. This layer may be the culprit.