To start the process they usually have the planes that outline the area that they are going to fill up. That's when you see them with the short trail that 'disappears' right away. I believe that their devices can detect the boundaries that they set up- then they just go back and forth and fill that area up. Sometimes if there's no currents the 'clouds' stick around and sometimes they drift here and there. When you see the 'clouds' in that dappled pattern that's when they shoot is with the HAARP arrays to organize the material into a solid piece, then it goes through a process and eventually becomes rain and snow clouds. They can keep it grey outside for days on end in certain conditions, eventually there are storms, and they can agitate the storms with HAARP and turn them into disasters. There are also thousands of stations that do nothing but pump water vapor into the air.