What kind of weather is caused by warm air rising?
Well, all warm air likes to rise. And if it is warm and humid air (like we have in the summer), it can result in rain and thunderstorms.
Warm air is "lighter" than cool air . . . and humid air is "lighter" than dry air (although most people don't realize this fact about humid air). "Lighter" air tends to rise above "heavier" air.
So if the air is both warm and humid, it tends to be very "light" and tends to rise easily.
Now, here's the tricky part. As air rises in the atmosphere it also cools, since usually the higher you go in the atmosphere the cooler the air at the higher levels above the ground (that's why very tall mountains have snow on top!).
So the warm-and-humid air is cooled as it rises. Also, remember that humidity is produced by water vapor, which is an invisible 'gas'. Eventually the warm-and-humid air cools so much that the vapor becomes water droplets (this is the process called condensation). In fact, clouds are really just millions of water droplets clustered together in the air.
If enough water vapor condenses into these tiny droplets, some of the droplets will merge with other droplets and grow into full-sized raindrops. You know what happens next!
Hope this helps!