Hitting the river at the right flow can have a significant impact on your fishing success. If you check the river flow shortly after a hard rain, you will notice a significant increase in the flow. This isn't the best time the go fishing. If you wait until the flow starts decreasing, or levels out, you will have much more productive day.
Wind can also play a big part in your ability to place your casts. Furthermore, if you plan to visit a lake, a heavy wind can blow you to the other end in a matter of minutes.
Check out the links below for river flows and weather forecasts for the area you plan to visit.