They rely on their keen senses of sight and hearing to survive and rain storms wreck havoc on those systems, that's one reason why it is so very common to find them flocked together in open fields, pipelines, etc...during rain storms. Their hearing is impacted by the rain, and the falling rain in the hardwoods causes tremendous amount of foliage movement that negates their keen eyesight, so they gather and move to open space as a survival tactic....depending on the severity of the storm, many will stay on roost or fly to roost for added safety.
If you want to hunt then in the rain, don't sleep on setting your blind right in the middle of a field or pipeline...I know it's not a common tactic as so many are brainwashed that blinds have to be brushed in and while that is certainly true with some big game animals, not the case with turkey. You can pop one up in the middle of a field and they'll stroll right by sometimes even more at ease than if you tried brushing one in to an edge. Decoys certainly help as well and are often more important than calling in these situations!
