In this case the weather definitely wouldn't have been a surprise. Based on where they turned around, I'm sure they carried additional fuel for exactly this possibility. I don't think a typical IFR fuel load would have allowed a turn back that far into the flight plan. I'm not sure what alternates were being used out east, but it very well could have been a commercial decision that they would rather have them turn back to Calgary and try again the next day rather than end up at their alternate, taking fuel, potentially running into duty day issues, and any other thing that could come up.
Sitting on the airplane for an extra couple hours is probably the least inconvienient thing that could have\would have happened.
Having said all of that it is kind of rare to have a turn back that far into the flight plan between two cities like Calgary and Toronto. I also have no idea how Porter's operation runs, so there could be other factors as well.
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