I can't say I understand it but the only line I can draw as far as references go is that Genbu is associated with the direction North and the season Winter. It makes me think Genbu is trying to say he's making a comeback or something...(my 5 cents)
I don't get it and I have read those books. Is Genbu a black brother? or maybe a white walker? I don't believe it is possible for it to snow in sky so I'm confused.