I know this has nothing to do with your question, but I'll chime in anyway.
Rain almost never closes the 3 outdoor zones, although Werewolf Canyon closes pretty easily in rain. Fright Zone can be prone to flooding, and that can close the zone, although I can only think of twice that has happened in the last 4 years. It takes quite a bit of rain to cause that. If it's a light rain at 8:00, everyone will be out. If it's heavy, they'll either open the zones late or put all the Screamsters in Fear Faire.
The most recent forecasts I've seen no longer call for any rain on Friday or anytime this weekend, so you should be good to go.
-Chris Woodard
2004 Screamsters, 2005 & 2006 Screamsters and Admissions
2007 Screamsters, Admissions, Corkscrew, Millennium Force, Monster Midway Invasion
2008 Ripcord/Skyscraper, Screamsters