Nottingham Forest faced a lot of huddle's before getting to that point, as it's stands now they are very formidable, so it's highly possible that they can maintain that position. Whatever inconsistent you feel they will face, also place it on Manchester City too as they are not going to get an easy ride too because even the least Club you didn't expect can disrupt your plans. I agree with that Nottingham Forest will qualify for the champions league as they've already positioned themselves in an advantageous position at the moment.
Nottingham Forest really showed that they can compete at the top this season, they showed a good game and are now in 3rd position, I hope they can maintain it until the end of the season.
But more than that I expect them in the next season they can maintain their good performance like this. Because usually teams that were previously not too strong like them, in the following season they have to experience a very deep decline so that they have to return to not being able to compete at the top and can only compete in the middle.