What Is Pressure?
Atmospheric pressure is also called barometric pressure because barometers are used to measure it. Atmospheric pressure, barometric pressure, and air pressure all refer to the same thing: the weight of the atmosphere at any location, generated by the downward force of gravity. Pressure decreases with increasing elevation because there is less air above you.
How Is It Measured?
Electronic pressure sensors used in AcuRite products and most home weather stations measure pressure changes through device that includes a quartz membrane secured over an evacuated chamber. As this flexes with changes in pressure, it measures the strain due to an applied force over an area. The output of voltage fluctuations are then converted to digital to be used on home weather displays or your online apps and weather dashboards.
Why Do I Care?
Atmospheric pressure changes occur with large-scale high and low pressure systems moving across the Earth. High pressure generally implies clear skies and uneventful weather while low pressure generally implies clouds, precipitation, and active weather. Most home weather stations can help you understand what weather is on the way by tracking the pressure trend.
One pressure measurement alone doesn't help meteorologists understand the weather, but if we have multiple readings of increasing or decreasing pressure values, then we can have some idea of the forecast. Increasing pressure tells us higher pressure is coming and skies will clear up, while decreasing pressure signals a low pressure system is on its way bringing clouds and possibly rain.
The warm and cold fronts accompanying these high and low pressure systems are what trigger rain and severe weather events. You may recognize this image from the National Weather Service, similar to weather maps often shown by your local TV meteorologist. You will see precipitation along and ahead of the fronts associated with low pressure, while generally uneventful weather accompanies high pressure systems.