I have a choice of tent camping in Yellowstone in mid August or mid September for two weeks. Which would be better? Is the weather a problem in September? My trip is for two months starting the first part of August.

My personal preference for visiting the National Parks, particularly the popular ones, is in September. It's still summer, but the kids are back in school. There are less crowds, and you can better enjoy the parks. I'd still go prepared for weather extremes, not that you'll likely see snow, but cold rains and storms are not out of the question. Don't let that discourage you though, because it's during these extremes that Mother Nature tends to put on her best displays.