Over a period of a year, one of Jupiter's two main dark belts has faded completely away. The South Equatorial Belt (SEB) is gone, leaving just the north belt (NEB) viewable in small telescopes. Credit: Anthony Wesley

Jupiters belts do however have a cycle in which they fade and return. This cycle have a period of 15 years, so the belt should return in a couple of years, if everthiings is as normal.

While the dissapearing act was a pretty undramatic fade-away, the return is usually more dramatic, whih a lot of storms and turbulens.

Source: The Planetary Society Blog