Philly suffers from the "urban heat island" effect. (high amounts of exposed asphalt, concentration of old buildings/black rooftops, congestion of cars/trucks) Nothing they can do about it. If Philly's landscape was similar to the burbs they would have no where near the amount of 90 degree days as they do currently. So in essence Philly's high temps have much to do w/environment along w/weather...
85F/ DP 70F