I talked to somebody today who insists that he can predict the weather months in advance, to the point of giving specific dates (within a day or two) when we’ll get specific amounts of rain. He’s also warned me of a couple of impending hurricanes, one to hit Florida in early September, and one to hit the Gulf Coast in early October. This person also insists that different government agencies have considerable (although not total) control over the weather. According to him, just about every rain we get in Central Texas is somehow enhanced by cloud seeding, and the controlling agencies have the capability of making the rain fall over particular places: streams and rivers that feed our reservoirs in particular. The guy seems pretty normal (I’ve known him for about 18 months), but he has some crackpot ideas.
There is some evidence that cloud seeding (both rain enhancement and hail suppression) are effective, but the evidence is hardly conclusive. Weather systems and rain clouds are sufficiently complex and variable that it’s difficult to determine if the observed effects are caused by cloud seeding, or just “noise” in the systems’ natural variability. This web site contains a good introduction and discussion of different cloud seeding techniques and their effectiveness. There are those who claim that our ability to modify weather is much more than what the government lets on.
A 1996 US Air Force Research Paper titled Weather as a Force Multiplier: Owning the Weather in 2025 explored some of the possibilities and problems of large scale weather modification. It’s an interesting read, but more of an academic exercise than practical research. That doesn’t prevent conspiracy theorists from insisting that the things discussed in the paper are actually being done today. There are some private companies (Eastlund Scientific, for example) doing research in this area, but nobody serious is claiming the ability to change the direction of a thunderstorm or hurricane.