I appreciate this is about legality, but you then mentioned it happened in reality and a choice had to be made. Legal or not "common sense rules, OK". Surely, when-ever you are inbound to a dodgy wx. destination you'll have a cast-iron alternate, or 2, up your sleeve. It's not the legality of the matter about the alternate, it is about getting on the ground, preferably on some suitable tarmac, still with some fuel in the tanks, and at a place where more fuel is available. Planning is before the event, airmanship is in the execution of the event.