You realize localized weather is not always predictable far enough in advance to do much? Moreover, airlines don't require passengers specify their weight when they purchase a ticket, so they can't really plan ahead for going over a specific weight that is itself tied to local weather conditions. Mind you, this could be avoided by building in more wiggle-room, but that is not going to be accepted as a solution because it results in waste much of the time if, for example, you have empty seats because you wanted to be sure that you wouldn't run in to the issue of going over weight.