This is the Great White Spot of Saturn (see top left of the image), which began as a “fluffy white storm cloud” in the northern hemisphere of Saturn back in 2010. Now, it has spread across the entire planet, which, if scaled to a storm system on the Earth, would be comparable to “a storm system that covers all of North America but wraps around the entire planet.”
Pictured here in false colored infrared in February, orange colors indicate clouds deep in the atmosphere, while light colors highlight clouds higher up. The rings of Saturn are seen nearly edge-on as the thin blue horizontal line. The warped dark bands are the shadows of the rings cast onto the cloud tops by the Sun to the upper left. A source of radio noise from lightning, the intense storm was thought to relate to seasonal changes when spring emerges in the north of Saturn. After raging for over six months, the iconic storm circled the entire planet and then tried to absorb its own tail -- which surprisingly caused it to fade away.
(Image Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA)