I'll dito the comment JohnS made. I've used dino 5w30 to -30F with no problems. For all the panic people make about needing synthetic if it gets below zero, its amazing all the engines in MN haven't up and died yet (or don't start in the winter).
I know its a few months 'til winter, but humor me . Lets use Chevron Havoline 5w30 as an example, because at 5300/@-30 its a very good cold cranking dino. At what temp would you think that its best to switch to a PAO syn? We sometimes experience temps of zero F to a few degrees below for a couple of months here in East Ky. If it helps, my wife's '03 Calalier manual suggests syn only at -20 F.