I would aerate now and add amendments to fill the plugs. And then I would seed the first part of September. Back off the nitrogen in your lawn food though.
Snow, if it is deep enough, can actually serve as a good insulator. You want your lawn seed to germinate and be on its way to establishing before frost dangers and certainly before any ground frosts.
Perennial ryes will germinate in about 7-10 days but fescues and bluegrasses can take 21 or more days under ideal conditions. If this puts you in danger of frosts or severe weather you may want to wait until Spring?