Arch-Diocese of Galveston-Houston....
Size: 1 million+ Catholics, 150 parishes, many languages/sizes, 8th largest Diocese in the United States
Culture: As variable as you can imagine! The Houston-Galveston area is one of the most diverse in the nation. Houston has cultures from all over the world. We have an obviously large (maybe not to someone not from here, heh) Hispanic (Mexican immigrant, primarily) population. As such, many parishes (not all by any means) have at least one Spanish mass.
There's also some very large populations of Indian (from India, not Native Americans) and Vietnamese here. Along with that comes some GREAT and very authentic food from around the world. Houston is known nationwide as the most eating-out city in the U.S. You can eat out every night and eat something different every time.... Or, you can do what I do, which is eat Mexican almost everyday and never get tired of it. If you've never had Mexican (or Tex-Mex) down here, then you have no idea what Mexican food is

.... There's also populations of Greeks (including a Greek part of town with a Greek Orthodox church), Chinese, Arabs, and Jewish.
We have some very well-off areas (say... Sugarland/First Colony, The Woodlands, Kingwood, and nicer parts of Houston, such as River Oaks and Memorial), and some very poor areas both rural and inner-city, along with everything inbetween. No, we don't all wear cowboy hats and own horses (very few do either), but there are a ton of pick-up trucks.
Weather: Well, when we get temperatures under 32 degrees F overnight, everybody freaks out and they put "FREEZE" on the weather headlines, heh. It rarely (once every few years) stays below freezing for any significant period of time once the sun is up. We will have temps in the 70's this week during the day. In the summer, it will get quite hot, but not desert-hot. Generally, the weather is pretty good, if you don't mind heat and higher humidity during the summer months. Non-summer months are extremely mild. We had our first snow this year in about 14 years, and it only lasted one day. The only bad side, is when it rains it REALLY rains... We don't get sprikles, we get mini-monsoons.... But it's par for the course. Nobody gets frazzled over it.
In general, I'd just avoid Galveston altogether (the only reason it's the Arch-Diocese of Galveston-Houston is that Galveston developed first, and was originally the Diocese of Galveston.... Houston was added later, but is now the 4th largest city in the United States. Obviously dwarfing Galveston).
Besides its population density, Houston is also, in square miles, the physically largest city in the United States. So, be sure if you were to move here that you thoroughly investigate which part of town to be in. "Across town" can be 60 miles or more. Thankfully, we have the most elaborate freeway system outside of Los Angeles, and arguably, a much better system than any city of this size, especially L.A.
The parish I attend (in Sugarland, a nice suburb of Houston on the southwest side), is pretty awesome. Attendance is in the 7,000 per weekend range, and there are many similarly-sized parishes around, along with many medium-size and smaller parishes. In Texas, there's anything you could possibly want.
God bless,
Michael