pricey,
Turn it up mate LOL. I love Melbourne more than the next bloke and I lived there for 35 years but it sure does go below 14 degrees a hell of a lot of the time and that's not counting that bloody wind chill factor.
Regardless, weather is a really important issue. Also, you need to think about what happens at somewhere like Northwestern when it snows. Do they have indoor facilities? Do you even want to practise indoors when you play outdoors 99% of the time? Little things, but they do add up and shouldn't be overlooked.
Tennessee is a lot more like our climate but doesn't have that mad spike up into the 30's and low 40's.
When do you need to make a decision by ?
All serious tennis schools in colder areas of the country have good to great indoor tennis facilities. Those schools definitely play outdoors less than 99% of the time.
During the fall season, schools will generally play outdoors (unless it's raining) and will often travel to warmer climates for fall invitational tournaments. After the winter break, from January through March, those colder-climate schools will play all of their home matches indoors. If they visit another colder-climate school, those matches will be played indoors. If they travel down south or out west for a match, those will generally be outdoors.
Once spring comes, and depending on how far north the school is, matches will be played indoors or outdoors depending on the weather. It's not unusual to get days of great weather at the end of March or beginning of April and play a match outdoors, only to have the weather get bad again and go back indoors. Usually by the middle or end of April, those colder-climate schools will start to play consistently outdoors through the end of the season, unless its raining.
My only point is that for these schools, indoor tennis is a dedicated part of the season. It's not like they're running into poor indoor facilities on the off chance the weather will be bad. They know it will be bad for part of the year, so they have the facilities to accomodate that fact. Since their conference opponents are in the same region and are also colder-climate schools, they will often play several indoor matches in a row. Not to mention the fact that for the best tennis schools, there is the National Team Indoor tournament.
I would totally understand if a player had a preference for living in a warmer climate. I'm just saying that if they choose to go somewhere colder or only have an opportunity to go someplace colder, there are good facilities to accomodate their tennis.