After searching for that, I did find results, but none on the uspto.gov website. If there are indeed US patents filed for weather modification chemicals, I wouldn't be surprised if they are some sort of distraction. I.e. the oldest magic trick in the book - watch this hand over here, don't worry about what the other hand is doing behind the back. If people are spending all their time trying to figure out what is going on with the publicly listed patents, then that is less people trying to find the real research.