The Definitions of Temperature, Dew Point and Barometric Pressure

Meteorological weather indicators help scientists understand current weather conditions and predict future patterns.
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Scientists use temperature, dew point and barometric pressure to understand and describe weather. Together, these three common indicators summarize complex weather information in a format that's easy to grasp for meteorologists, climate scientists and the general public. Standardized weather measurements like these help scientists understand -- and potentially predict -- future weather patterns.


Temperature is usually measured in degrees Celsius using the metric system (degrees Fahrenheit in the United States). Air temperature measures the amount of movement in the air's atoms and molecules. Air molecules move more quickly when they are warm and more slowly at cooler temperatures. As air molecules collide with a thermometer, the device measures how much energy is transferred to it (if the air is warm) or pulled from it (if the air is cool).

Dew Point

In simplest terms, dew point is the temperature at which air would be saturated with water. Warmer air can hold more water vapor than colder air. When air is holding all the water it can hold, it is said to be "saturated," and its relative humidity is calculated at 100 percent. Dew point temperature is never higher than the air temperature. When air cools, moisture leaves the air as condensation -- creating weather conditions that are cloudy, rainy or snowy.

Barometric Pressure

Barometric pressure, also called barometric air pressure or atmospheric pressure, is a measure of the weight of air molecules as gravity pulls them toward the earth's surface. That pressure changes as local weather conditions change.

Scientists measure barometric pressure using many different units. Meteorologists tend to use metric bars, millibars or Pascals. Some scientists also use atmospheres or inches of mercury, especially in the United States. For comparison, the following measurements are all equivalent for sea level at zero degrees C: 1 atmosphere, 29.92 inches of mercury, 101,325 Pascals and 1,013.25 millibars.

Using Meteorological Measurements

A convergence of temperature and dew point indicates nearly saturated air that's likely to condense into clouds, fog or rain. When the two measurements are farther apart, air is less saturated and dryer, resulting in lower humidity.

High barometric pressure generally translates to clear weather, though it may indicate winter snowfall under specific conditions. Declining pressure signals the arrival of a low-pressure front, usually heralding precipitation and cloudy weather.

Understanding simple measurements like these allows meteorologists to predict upcoming climate events. Together, temperature, dew point and barometric pressure represent three of the most versatile implements in the climate scientist's toolkit.

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