Humidity is the amount of moisture present in the air, and it can change depending upon the time of year and whether there is active precipitation. Relative humidity is the percentage of moisture that actually exists relative to the amount that could exist. Dew points reflect the temperatures where 100% humidity will occur.
There are certain regions that tend to have higher levels of moisture in the air than others. In general, cities that are located closer to the equator have higher dew points and feel more humid. A muggy feel is common in these cities, especially in the morning. Cities with high humidity and low dew points have more of an arid feel to them.
Air moisture is a key component of this measurement. When there is more moisture, there is a greater chance of precipitation, and storm activity tends to increase. For example, locations such as Florida in the United States tend to experience regular afternoon thunderstorms year round.
Cold air is not able to hold as much moisture. In many locations, cool morning temperatures often result in visible dew on plants and grass as the air releases water that it cannot hold.
Relative humidity indicates the percentage of air moisture. For example, a measurement of 30% relative humidity might indicate low levels, while 50 or 60% would indicate high levels. When precipitation occurs, these percentages typically approach 100%, which indicates full saturation.
The thickness of the air tends to be greater with higher levels of moisture. Besides a general feeling of mugginess, these higher levels can also make warm or cool temperatures feel more extreme. In humid locations, warm temperatures will feel warmer than the same temperatures in an arid climate. Likewise, cool temperatures in humid locations will feel much colder than the same temperatures in a dry area.
An example of this phenomenon can be seen in a location such as Florida. Residents of this state often put on sweaters and turn on their heat with temperatures as high as 50°F (10°C). The same temperature in a drier climate, such as the state of Colorado, might prompt those residents to turn off their heaters.
Coastal breezes can diminish the feeling of humidity. The breeze helps to circulate the air and remove some of its heaviness, while cooling temperatures. Cities that are located inland tend to maintain a stuffy feeling.