Weather should be one of the last things on your list when considering.
In the event that you do get accepted to more programs, your next step should be to visit. Meet professors, meet graduate students, talk to people. Ask questions about funding packages, placement rates, and time to degree. Go into the academic buildings, visit a lab, walk around the libraries and study spaces. Walk around the neighborhood of the school and look at apartments, if you have the chance (Craigslist.com is great for looking at prices). Visit some cultural institutions. I think a 2-3 day trip for each school is sufficient enough to get a little snapshot.
Then sit down, and lay out this information about each school:
-How is the research fit? Am I going to be able to do something close to what I want here? Will I be bored out of my mind doing my dissertation?
-How are the professors? Do they treat students like junior colleagues or like research slaves? Am I okay with being treated like a research slave for a better chance at a top tier job, if need be?
-What's the funding like? Am I going to be able to live on that funding in this city? How much will I have to scrounge? What percent of my income will the average rent be?
-What are the university's facilities like? Are there places for me to study? Where will I work should I attend - a shared office, a cubicle, in my own apartment because the department has no place for graduate students? What are the libraries like? Will I have access to the works in my field that I need to get my work done?
-What is the average time to degree? Do most people get done in 5-6 years or are people languishing around for 7-8? How many people leave the program before finishing? 20%? 50%? 70%? (Some departments don't track this information, or don't track it very well.)
-Where do people end up after they finish here? Do people go straight into great tenure-track jobs? Do they do a postdoc for a few years and then a t-t job? Do they go into industry? Are they working in postdocs for years and years with no end in sight? Does what recent grads do match up with what I want to do?
And after you answer those questions and compare and eliminate schools based on that, THEN you can start asking and answering the location-based questions. But even then, I'd say the weather is towards the end of the list. You can always buy a coat/space heater or an air conditioning unit and some shorts. Things that are far more important are what kind of neighborhood you might have to live in, what rents are like in the area, what the cost of living is like, whether there are cultural institutions you like to visit nearby, whether there's a gym on-campus or nearby that you can afford if you work out, etc. If there's a specific hobby you like that requires something special (like hiking or kayaking) you may want to see if such facilities are within proximity to the school.
I mean, you don't want to be miserable where you are, but 5 years is not a very long time and you'll be spending the majority of it studying intensely for a degree. Actually the fewer distractions you have, probably is the better.