The trick is to have the "base top" be something that is decent enough you can walk around in outside. Then wear a layer over it to be comfortable and more professional while inside the convention center. You'll see lots of summer dresses with a layer on top. Depends on how professional you need to be, but capri pants can also be a cooler options - yet warm enough you don't freeze inside. For the layer - its tough to predict because it will depend on how quickly you get cold/warmer and the temperature that day at the convention center. I would bring some that are lightweight and one that goes with everything that is heavier.
Sandals you can walk for miles in are also important. Also needed - if you are going to go straight from a meeting to dinner offsite with convention goers, if you aren't going to have time to go to your room, you'll need a bag that maybe that layer can be shoved into.
I've been there twice for conventions - once late spring and once mid-fall. The temperature was NOT consistent in the convention center. Somedays (and locations) seemed too cold, and others were surprisingly warmer than expected. Probably a range of 67-74 degrees.