The factor in the atmosphere that is most responsible for changes in an area's temperatures and humidity levels is the movement of large air masses.
Air masses are large bodies of air that have similar temperature and humidity characteristics, and when they move, they bring changes in weather conditions, including temperature and humidity. For example, when a warm, moist air mass moves into an area, it can raise temperatures and humidity levels, while a cold, dry air mass can lower both.
While factors like cloud formations, air density, and precipitation do influence weather, the movement of air masses plays a more direct role in the overall temperature and humidity dynamics of a region.