Well to aviod lines go during the week and not near holidays.

: )

Sundays during summer are the absolute worst day to go! They have horrible lines. Yet, you can buy a flash pass, and that gives you almost to wait. I would go on a tuesday, wednesday or thrusday. weatherwise, i would nee to know which sunday you mean. Still, six flags great adventure is great!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! make sure you ride the kingda ka, and medusa

I will be there in less than 12 hours =P

In order to avoid bad weather, you have to check the forecast because you can't really tell when it's going to be nice out or not. It's best to go during the summer, though. As for long lines, you should definitely go on a weekday, rather than a Sunday. Weekdays are usually less crowded.