Think about when you are most likely to see turkeys out and about when you take a drive through the countryside... in my experience that is while it is raining.
Turkeys are more likely to be in a field during a rain than anywhere else. I once snuck up on a strutter, who was out in the field about 20 yards from the timber edge, and he was so wet his fan looked like pickup sticks and not feathers. It was a peculiar sight to be sure, I then whistled an arrow just underneath him, leaving a few wet feathers behind as a memento. Oh well, the stalk was awesome, the shot was very bad!
They will tend to be silent and will flock up a bit more in the rain, but if you know of an out of the way open field they are comfortable using, I would camp there. This is also a nice time to stay inside a dry blind too.
I have also noticed that if it is raining at fly down time, they will tend to stay on roost longer, perhaps an hour or longer than normal. I have shot them in the rain several times before, but be prepared for a patience game, wait them out. I have also had them start gobbling nicely at the sight of the sun coming out after a rain too.
One other factor... if rain/thunderstorms are imminent I have had them come in faster than normal to calling. It is almost like they want to get "hooked up" before the weather sets in. I would not recommend staying while it is lightning of course, but over the years right before the storm hits we have called in some very nice birds and quick.