Regarding scripting. There must be a line of code somewhere that defines AP Fair Cloud as the weather pattern when choosing cloudy in quick drive.
There are 7 weather types defined in kuju/trainsimulatorcore/weather that are used for the QD weather. They all start with rw_ (e.g. rw_cloudy). They can be replaced by any weather definition built with the weather blueprint, also changing weather situations (e.g. from clear to rain). This is what AP does when you install it, it replaces the kuju QD weather with its own by renaming them (e.g. AP Fair Cloud to rw_cloudy).