There are quite a few ways to imply that someone is stupid without just coming out and saying it straight out. “Not playing with a full deck”; “Ain’t got sense God gave a goose” and “A few bricks shy of a load” are some examples. The most pervasive one I’d heard as a child was, “He hasn’t the sense to come in out of the rain”.
That saying does seem to be one of the top sayings in the U.S. concerning a lack of mental ability. There’s an article about regional phrases, 9 Ways of Saying "Stupid" and this survey about regional idioms. Both seem to indicate that not coming in out of the rain is rather universally suspect.
So if everyone agrees that people shouldn’t stand out in the rain (or a hurricane too, maybe), why do news organizations make reporters do just that?
And then there’s this:
No DUH!