Does the adjective garbh not add an 'h' after cho, as in gharbh?
can this only be used to describe the weather or could you also say that as in 'this math topic is so rough'
It doesn't just have to be the weather it can also be water (like the sea) or rough ground, but I don't know about maths lessons! We'd usually say "tough" for that in Scots English, not "rough".
What about "I'm feeling pretty rough this morning"?