A city is a huge heat sink; retains heat long after the source (sun) has passed the horizon. The first time I really became aware of just how much heat the concrete jungle retains was during a night time drive in a convertible. The night was clear, almost cold, yet upon crossing some imaginary line (3 or 4 miles) from the city the temperature jumped several degrees warmer.
Many if not most of the reporting stations for local news stations are located within the cities boundaries which IMO will always report a warmer
I grew up on a small 40 acre farm 7 miles from the closest city and our temps (according to our temp gauge) was always slightly cooler during the
summer and colder during the winter.