Heavy rain might keep them from moving around and lower your chances.
However, spring turkey season this year, on the last Saturday of the season, it poured rain all morning. The guy I hunt with, him and I hung out in the truck until about 10am and finally decided the rain wasn't going to stop and the day was a wash. Anyway - we figured we go ahead into the woods and set up our blinds because the rain finally slowed down to a drizzle. At that point, we figured we'd return on Sunday and hunt the final day of the season. We grabbed our stuff, I left my gun in the truck but told my buddy to get his just in case. So we are walking this open ridge top and I'll be damned if a big old turkey wasn't "nesting" in the middle of this open field in the rain. We drop out of sight, my buddy crawls 50 yards to a feed trough, pokes his head over it and the turkey is still there. A couple of minutes later the turkey gets up, gives my buddy a shot and we are eating fresh turkey a few hours later.
I know that's a long way of saying the rain will lower your chances some, but you never know. It's always worth a giving it a try.