Wind mixes air from above down to the surface. This brings warmer air in two ways. First, air aloft is usually warmer at night. This is called an inversion. Air is cooled from the surface up at night, and winds can mix that warmer air aloft down. The other way descending air causes warming is because of thermodynamic effects. When air descends it is compressed. As a result, the temperature increases. The nighttime cooling finally took effect after 3:00.