I'm not sure bout the weather but I think age has something to do with it. I think the later they are born in the year the later they shed velvet. I guess more mature bucks probably aren't affected by their birthday but the first and second years they probably are. Seems like they shed at different times too. I killed a nice 8 pt last year that shed an antler when he piled up after I shot him. The other side came off in my hand when I was checking him out. That's a real bummer too because he was probably the widest buck I have ever shot. I got him on the first day of the Christmas hunt. I saw a buck in late Feburary or early March that still had horns.