Moreover, land masses heat and cool more quickly than oceans. In winter, the cold terrain chills the air, its density increases. The pressure increases and we call that a high pressure area. Conversely, the warmer air has less pressure. If water vapor is added, the density is further diminished so that when the air rises, it accelerates.
All air movements can generate or dissipate clouds.
Pressure differences result in temperature differences and produce moving air. Heating air makes it rise, and cooling air makes it sink. Air moving from a high to low pressure creates moisture, which condenses into clouds or fog. When moisture-laden air is cooled, its ability to hold water is greatly reduced, resulting in condensation, rain, snow or fog. In summary, relative humidity is the comparison of how much water vapor air holds relative to how much it could hold.