Water vapor is an invisible form of water in the air. Warm air can hold more water as vapor than cold air. When the air temperature falls to the dew point temperature, dew will start to form on surfaces or fog can form in the air. Dew point temperature is, in effect, a measure of the amount of moisture in the air. If the dew point temperature is much lower that the air temperature, the air is dry.
Temperature never falls below the dew point temperatures.
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