Tying this all back to the population trends:
If you are in the Midwest the advantage to moving South is that you get less snow or, if you go far enough, you can "throw away the scraper" as Brad put it. However, for most (ie, not
@Riffraft ) people that advantage is at least partially offset by the fact that you get an increase in uncomfortably hot months.
Moving say from Chicago to Atlanta you'd get an increase in uncomfortably hot months and you wouldn't actually be able to throw away the scraper. Obviously you'd use a scraper less in Atlanta than Chicago but the average daily low in Atlanta is only slightly above freezing in December and January so you probably wouldn't want to get rid of it entirely. It DOES occasionally snow in Atlanta. Worse, they get ice storms. Worst still, they simply don't have the equipment and infrastructure to handle it the way that places like Chicago, Detroit, Cleveland, and Buffalo do so when it does snow it is a catastrophe. Also, don't ever drive when it is snowy in the South, those people have only limited experience with it and they have no idea how to handle it.
Costal California is basically a "cheat code". Both LA and SF have warmer winters than the Midwest, so warm in fact that you can "throw away the scraper" and they actually have cooler summers than Chicago so you basically have the best of both worlds.
Looking at population trends, this all makes sense. California's population growth took off well before Texas, Florida, and Arizona. That makes sense because California was "livable" before a/c. What a/c did for California was to open up the interior for development. As noted, LA and SF have pleasant summers but if you get 50-100 miles inland (depending on topography it can be more or less) you are basically looking at Arizona's climate and only Riff wants that.
Texas', Florida's, and Arizona's population growth didn't really take off until after a/c was widely available in private homes. In the half-century from 1920-1970 Texas' population only grew from a little below Ohio's to about equal to PA/IL/OH. In the half-century from 1970-2020 Texas' population exploded to more than any two of PA/IL/OH.
I'm still at a loss to explain Pennsylvania's decline at least relative to Ohio and Michigan. I think that
@betarhoalphadelta 's theory that major Cities like NYC and Chicago draw people from the entire region not just the state explains PA's decline relative to NY and IL but, as I see it, Philly and Pittsburg aren't substantially less of a draw than Detroit, Cleveland, Columbus, or Cincinnati.
Here are some numbers to illustrate the change: In the late-1800s and early 1900s Pennsylvania's population was around half-again Ohio's and around two-and-a-half times Michigan's. The peak for PA relative to both OH and MI was in 1910 when PA's population was 161% of Ohio's and 273% of Michigan's. Ninety years later in 2000 Pennsylvania's population was only about 8% more than OH's and 24% more than MI's. It has recovered a little in the last two censuses but it is still only about 10% over Ohio's and 29% over Michigan's.
