For whatever reason, what I remember most about 9/11 was how beautiful the weather was that day.
September has always been my favorite time of the year, partly due to the return of football (although September of 2001 was a bad, bad month for us), but partly due to the weather. On Labor Day, it's usually hot and sticky, but by the middle of the month, fall starts to appear, and you therefore experience those gorgeous days where it's 70-something degrees, there's little humidity, and there's not a cloud in the sky. 9/11 was one of those days in Pennsylvania.
I've never been particularly eloquent, so I'll just say stop here: whenever you're sitting in Beaver Stadium during a beautiful September day, remember those who aren't there to experience it and remember those who lost friends and loved ones on that beautiful September day.