There are communities larger than you'd expect around just about every topic imaginable. I'm certain there are temperature enthusiast groups, especially given its adjacency to climate stuff. It's probably going to be people mostly betting on something they have better than average knowledge of. I'd be interesting to compare the 'normal' majority temperature predictions from polymarket to local weather station predictions. I'm betting polymarket wins, by a wide margin.

For instance chess wagers on polymarket are super interesting because it's far more informative than a chess engine, even though engines are much stronger than any human. The nuance is that engines don't appreciate human factors like how easy/hard a position is to play. And so an engine might just say 'dead draw', whereas a strong human can say 'nah, white has very good winning chances here' - and the polymarket wagers end up reflecting that. And so there it's mostly strong players making money from people who think turning on their engine and betting based on what it says is something nobody else must have thought of.