I know in 2008 it was supposed to drizzle over the opening ceremonies of the Olympics so the Chinese did some weird thing with putting a lot of rice (or something like that) in the air to absorb some of the moisture so it wouldn’t rain.
I don’t think I’m allowed to post links here so I’ll just encourage those who are interested to research “cloud seeding” which is a method of weather modification that has been in use for many years – mostly using the method of releasing silver iodide into the clouds. Precipitation can be encouraged through that method.
However, things such as a computer than cause a tornado on an enemy’s territory are still relegated to SciFi movies.