Feast of Famine - Condition Verification

[Bombast]

I'm gonna use this thread so I don't need to make one. Can anyone explain me how the weather transition works? Do we need to fish the mooching fish on the first weather and then mooch it when it moves to the transitioned weather or we simple need that weather combo and fish it on the last weather?

You fish on the second weather pattern. So, for example, a Mahar (Which is mooched to get a Shonisaurus) can only be caught during a Blizzard, but only if that Blizzard was preceded by clear weather.

The first weather pattern is useless to you, besides the fact that it has to be there.