What is the dew point? Understanding the difference between humidity and the dew point.

Have you ever walked outside and the weather that can only be described as "muggy"? There are times when the humidity in the air becomes sticky and, on occasion, even oppressive.

This is where the dew point comes into play, but what is the dew point and how does it interact with humidity?

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What is the dew point?

The dew point is the temperature the air must reach before it can be cooled, at constant pressure, to achieve a relative humidity of 100%, according to the Weather Service.

In other words, the air will not be able to hold more water in its gas form. If the air were to cool even more, water vapor would release into the atmosphere in its liquid form, such as via fog, dew or precipitation.

The higher the dew point, the greater amount of moisture present in the air, says the Weather Service. When considering dew point levels, these conditions can be expected during the warmer months:

• Less than or equal to 55: "dry and comfortable"

• Between 55 and 65: "becoming 'sticky' with muggy evenings"

• Greater than or equal to 65: "lots of moisture in the air, becoming oppressive"

As a result, some days may feel more humid than others, even if the relative humidity is higher.

For example, a temperature of 30 degrees and a dew point of 30 will give you a relative humidity of 100%.

Therefore, a 70-degree day with 50% relative humidity would feel more humid than a 40-degree day with 100% relative humidity. This is the result of higher dew points, says the Weather Service.

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What is the difference between the dew point and humidity?

Humidity is more than just one concept. It includes absolute humidity and relative humidity.

Absolute humidity measures the actual amount of water vapor in the air, regardless of the air's temperature, according to the Weather Service. On the other hand, relative humidity measures water vapor and its relativity to the temperature of the air.

As mentioned above, the dew point is the temperature at which the air must reach before it can be cooled, at constant pressure, to achieve a relative humidity of 100%.

Relative humidity and the dew point work together and have an impact on clouds and precipitation, says the Weather Service.

When relative humidity is at 100%, (such as when dew point temperature and actual air temperature are the same), this means there is a maximum amount of moisture present in the air at that particular temperature. As a result, this saturation could lead to fog, dew, clouds and, in other cases, precipitation.

In order for precipitation to occur, the air must no longer be able to support the weight of the suspended water droplets, causing precipitation to fall from the clouds, says the Weather Service.

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What's the highest dew point temperature ever recorded?

According to the National Weather Service, the highest dew point ever recorded was 95 degrees Fahrenheit in Dhahran, Saudi Arabia, on July 8, 2003. The air temperature reached 108 degrees Fahrenheit, and the heat index was 178 degrees Fahrenheit.

The highest dew point ever recorded in the U.S. was 90 degrees Fahrenheit. This was recorded at the New Orleans Naval Air Station on July 30, 1987, and in Melbourne, Florida, on July 12, 1987, according to the Weather Service.

That mark was also reached in Appleton, Wisconsin, in 1995, when the accompanying heat index reached 149 degrees Fahrenheit.

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This article originally appeared on USA TODAY: What is the dew point? The difference between dew point and humidity