If it's heavy and wet, it'll help Novak. If it's hot and sunny, it'll help Nadal. This can be clear in their 2012 match up where the conditions were helping Novak in the 3rd set when it was heavy and wet, while the next day, which was sunny and hot, helped Nadal.
Heavy and wet means lower bounce, hot and sunny means higher bounce.
I see, chances of light rain tomorrow. More heavy and slower conditions, should benefit Novak.