From The Atlantic (yeah, I know) a not-too-terribly scientific look at what a terraformed Mars might look like. Great pics:
I can't imagine that doesn't result in some really odd weather. I do think the artist got it right that one half of that continent is really green (perhaps even waterlogged, like the Amazon) and the other half is pretty dry and barren; a watery Mars isn't necessarily going to be a green Mars. I could also see a wet Mars experiencing something like an epic version of our monsoon pattern weather.