Well, from the looks of it, the normal aircraft routing is GFK-MSP-PHL-MSP-RDU and the GFK-MSP and MSP-RDU flights are both ontime. Looks like there are a lot of 60+ min delays out of PHL. It may have been an operational decision to go ahead and keep the aircraft on time by cancelling the flight but it looks like the reason was the aircraft would have been delayed because of weather.