Le ciel est nuageux, le temps est nuageux, la météo est nuageuse. All of those are possible. Not "il est nuageux", unless you started your speech with something like "Par la fenêtre, je peux voir le ciel. Il est nuageux".
I still don't understand why la météo is not accepted in this case. If météo doesn't mean weather it shouldn't have been used in other exercises or its meaning should have been made clearer. Very poor.