ELI5: What causes turbulence?

Turbulence happens when air moves in a messy, uneven way, like invisible bumps in the sky.

• Air is usually smooth, but sometimes it gets pushed around by wind changes, storms, mountains, or hot and cold air mixing.
• Think of it like water in a stream: if the water hits rocks, it starts to splash and swirl instead of flowing smoothly.
• In the sky, these swirls and little air “waves” can make a plane shake or jolt.
• One common cause is warm air rising and cool air sinking, which makes the air wobble up and down.
• Another cause is wind shear, when wind changes speed or direction suddenly, especially near jet streams.
• Sometimes air gets bumpy when it flows over mountains or buildings, which makes spinning pockets of air behind them.