Latitude makes a difference too. Is elevation more important than latitude ?
Absolutely when you're not talking about that much latitude, especially in the summer months. Look at all the average highs from Richmond to Philly, they aren't that different from Atlanta or Charlotte. Compare Charlotte to Asheville, which are closer in latitude, but a difference of 1400' feet in elevation. This is a reason that areas above 3000' or so feet in the southern Appalachians are considered an Oceanic climate. High temperatures are much lower the higher you go, but the lows don't drop as drastically.