The velocity of air movement increases as it rushes around and over an object, and it can also create a dead air space on the leeward side of the object. Sites located near large bodies of water or rivers tend to be more humid than inland areas. Wind direction also affects humidity. Downwind from the water is more humid than up wind. Vegetation will also increase moisture in the air.
Water vapor is a gas that occupies the same space with other gases that together constitute air.
But in some ways, water vapor acts independently of the air. For any given temperature and degree of saturation, water vapor in the air exerts its own vapor pressure. It flows or migrates from areas of higher vapor pressure toward areas of lower vapor pressure in air or in materials. Moisture, driven by vapor pressure, can even travel through porous materials through which air cannot pass. The microclimate temperatures of the site may be different from the general data collected at the airport and can vary significantly at the site.