Molten Iron and hot sand - it's not easy to think of something more extreme than this:
http://www.nasa.gov/jpl/spitzer/brown-dwarf-20140107/
Add that to the high gravity of a small, dense Brown Dwarf. Theory predicts they can be as small as 0.75 RJup (if old enough) and much more massive.

I know, BDs are not planets. Howewer at some places, the boundaries are not well defined.
Then, I imagine that a high mass planet close to or even above what the astronomers define as the minimum mass for a BD could have a similar weather. Or could it not?

This mass could be anywhere between 10 and 17 MJ depending on metallicity and other parameters. I saw this numbers in a paper at arxiv.org - sorry for not remembering it's name now. And it seems there are planets (???) heavier than that in the net lists.