Extremely cold turbulence; it seems to be -220 degrees Celsius on Neptune. What weather system could thrive on an internal heat source producing such a small amount of heat?
It's almost like the weather systems have little to do with the planets, or their distance to the Sun.
Rotation is indeed something to consider; Jupiter, Neptune and Uranus (retrograde) rotate quite fast, but it won't fit. Venus "rotates" once every 240 something days (retrograde as well, could they be having the Neptune party together with Uranians?), and is hotter than hell.
Cheers.