The high temperature is usually recorded between 2:30 and 4:30pm, depending on whether it's Daylight Saving Time. At this point, the sun has had hours to heat-up the surface. A good portion of that energy has been stored-up by surface materials and is now beginning to radiate back into the air, heating it with great efficiency. A couple of hours after the sun angle has reached its highest point (late afternoon or early evening), the temperature usually starts to dip, as the amount of stored energy diminishes and the surface has less heat to release. An exception to this scenario would be when a cold front moves through our region during the day, ushering in a cooler air mass. In this relatively rare case, our daily high might well be struck early in the morning, prior to the front's passage.