Yep, this is legit. But the sports books that host these wagers aren't the most dependable...yet. You won't find this on fanduel or draftkings. There was one site I used to use for hockey that had this but it wasn't as easy as you would think. They would pick cities and do a max high temp or min low temp over/under but it wasn't "Philly's high temp 37 o/u"....you had a spread of say 34-42 and could take o/u for that range. Then if you wanted to wager within said range it would be like -1600 or something asinine.