Jupiter and Saturn, and to a lesser extent Uranus and Neptune, are known for the incredible storms that blow up in their huge atmospheres. Jupiter's Great Red Spot is no doubt the most famous. Bigger than Earth, it has probably existed since before Galileo became the first human to train a telescope on Jupiter.
Saturn lacks such a signature storm, but it has had a series of Great White Spots over the years. The latest was also the biggest yet seen. Observed by the Cassini spacccraft, that storm eventually expanded until it encircled the planet, and temperatures within the storm were at points 100 degrees F higher than in the surrounding atmosphere-- a huge amount of generated energy. That storm can still be seen, but it seems to be petering out.