Meteorologist elaborates on the sensation of humid air, referring to it as dew point.
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With soaring temperatures and humidity across parts of the United States, summer's early arrival is noticeable. When the dew point climbs, summer's muggy atmosphere becomes particularly oppressive. High dew points do more than just make us feel uncomfortable—they are essential in predicting the severe storms that plague the summer season.
The Role of Dew Point in Meteorology
In meteorology, the dew point is a measure of the atmospheric moisture level. It refers to the temperature at which the air becomes completely saturated with water vapor. The air must be cooled down to this temperature in order to reach the same level of saturation as the surrounding air at the current temperature.
"Once the air cannot hold any more water in its gaseous form, water vapor condenses into a liquid," explains meteorologist Cyrena Arnold from our website. "The warmer the air, the more water vapor it can hold."
Similar to dew point, relative humidity measures atmospheric moisture, but it is relative to the current air temperature, indicating the actual amount of water vapor in the air at a particular temperature.
A Bucket Filling Up
Just as a bucket can only hold a certain amount of water, air has a limit to its capacity for holding moisture. When the air reaches 100% relative humidity, it cannot hold any more water vapor in its gaseous state. If the air cools, water vapor transforms into liquid, usually appearing as fog or rain. When the air contains more water vapor than it can hold at its current temperature, it demonstrates supersaturation, resulting in the formation of clouds, fog, or rain.
High Dew Points and the Impacts on Comfort and Weather Forecasting
While low dew points mean less moisture in the atmosphere, which can cause dry skin or chapped lips, slightly higher or moderate dew points produce what we might perceive as a "crisp" feeling. Conversely, high summer dew points result in damp, stifling air.
The Gulf of Mexico plays a significant role in increasing dew points in the United States. Meteorologists can track dew points as they shift across the country.
"There's a reason why higher dew point temperatures are concentrated in the southeastern United States," says Arnold. "You'll see the ebbs and flows of the Gulf, moisture rising from the gulf, and then cold air from Canada moving back down."
The Importance of Dew Point in Weather Forecasting
The juxtaposition of high and low dew points is vital in forecasting the weather. Dew point provides insight into what the conditions will feel like outside, compared to relative humidity, which does not fully capture this sensation.
"If you observe dew points frequently enough, you start to grasp what 60-degree dew points feel like," says Arnold. "Relative humidity doesn't convey the same sense of humidity."
In addition to forecasting the weather, dew point plays a central role in predicting severe thunderstorms.
"Severe thunderstorms are more prone to occur when the surface dew point exceeds 55 degrees Fahrenheit," according to the NOAA. The four elements important for developing severe storms are wind shear, lift, instability, and moisture—or SLIM for short.
"There are no storms without moisture," underlines Arnold. "All four of these components are critical like puzzle pieces, but moisture is a crucial part of it."
The moisture aids in cloud formation and acts as fuel for thunderstorms, amplifying their power through enhanced updrafts. In terms of atmospheric dynamics, moisture contributes to rapid cloud growth, signaling the approach of stormy weather.
Understanding the moisture content in the air and the corresponding dew points helps determine the severity and danger of a thunderstorm.
"The importance of dew point in weather forecasting is truly astounding," says Arnold. "Although you may think it's just a measure of humidity, it involves complex thermodynamics behind the scenes."
[Note: For more information, read our article on why 60 degrees in fall feels distinct from spring temperatures.]
- In the realm of environmental science, understanding dew point is essential for predicting the weather, especially during summer when high dew points can result in severe storms.
- The meteorological concept of dew point is crucial in weather forecasting, as it contributes to the development and severity of thunderstorms.
