the only down side to rains is it allows the birds to flock back up so the a few days preceding the rains you will have big groups still until they start to spread again. every advantage comes with a disadvantage though. also one thing to keep in mind is if a big rain comes in at night most of the time birds will head to fields first thing in the AM regardless of what their normal pattern is, so they can dry out.
there are even a few theory's that turkeys can sense a storm coming and will roost in different areas due to the storm approaching.