Definitely No ! 오늘 온도가 이십삼도예요? is correct. 날씨 means the weather. I am a Korean The other one is 오늘 밖의 온도가 영하23도 예요.

hi, here's some casual way to say this for daily conversation. >to friends, younger people : "오늘 (바깥에/밖에) 영하 23도야?" >to elderly (respect language) : "오늘 (바깥에/밖에) 영하 23도 에요? / 인가요? / 입니까?(formal) It's like "Is it -23 degree (outside) today?" We usually omit "outside", "temperature" something like that in a conversation because "-23" already implies the temperature. If you wanna point out a specific place, you can switch the subject with a word like (저 안이, 방안이, 저 쪽은 etc) "차 안이 35도 에요??" - Is it 35degree inside the car?? "사무실이 25도 에요?" - Is it 25degree in the office?? Sorry, my poor english, i hope you got it.