I'm in the same boat as you. I am a Las Vegas native, and went to college in Phoenix..therefore I am VERY sensitive to cold weather. Basically anything less than 70 I need a light jacket
But generally, June and July the nights are a little cooler. From August through October it can be pretty hot during the day and therefore make the nights warmer. I would for sure bring a light jacket.
@theluckyrabbit suggestion of getting a locker is a good idea. If the night is warmer than you thought, then you can store them there. Also be sure to to check the weather. If the lows are showing 70's or 60's, a light jacket is needed. Without the sun that can make the air chilly.