I have an idea for a bending sub/ability for air benders: weather bending. People who are a professional or maybe skilled and professional at air bending can learn this sub element. They progress at it and learn new abilities/aspects just like with any main element. At first, all they can do is very strong wind. If they learn water bending, they can make a rain storm. If they learn air, water and lightning (not likely) they can make thunderstorms. If they learn ice/snow, they can make a snow storm, and after they get really good at ice/snow bending, a blizzard. You get the general idea. Also, if an avatar becomes godly at both air and water bending, they can make small hurricanes. I hope you use this idea!

Hmm
I like your ideas, but it fits into the natural bending cycles already,
A Blizzard can be made my a strong Water Bender, A Lightning Storm from a Lightning Bender by using enough fire to heat the atmosphere of a body of water to hydrate the air enough to create rain, followed by using Lightning to create the sparking touch. tornadoes can be created by Air Benders, and rain by Water Benders or Air Benders nead a body of water.

I was thinking, for rain, the person would bend a bunch of clouds with water in them together, and condense them, so they go from gas to liquid, more or less.

Noooo. In theory that would take all four bending elements combined, which is overly OP. And if you have an idea for a new bending element, apply for it in the proper section... .-.