Also like it was mentioned above, if you have problems as "Gay Days" is going on during that time, usually around the 7-9th then I would take that into consideration.
In 2007 Gay Days is scheduled Oct 5 - 7, which is Columbus Day weekend - Columbus Day is Monday Oct 8. So that extended weekend will be crowded.
Weather-wise the average high temp in October is 80 degrees, the average low temp is 56 degrees, and the average rainfall for the entire month is .26 inches.
Park hours are usually 10:00 - 8:00 during the week; 8:00 - 11:00 or 9:00 - midnight on weekends for DL. And 10:00 - 6:00 during the week; 10:00 - 9:00 on weeknds for DCA.