Thanks for clarifying. You're right! The output isn't actually text/plain. As someone who values standards, it is annoying to see control-code garbage when the content type claims to be text/plain. But wttr.in seems more like a fun novelty than a serious service and I suspect they don't pay much attention to standards. Still, I'm not sure that excuses saying one thing in the headers and delivering something else in the body.

But you've got a fair point. So thanks!