Weather forecasters use a special tool called a barometer to measure air pressure. Barometers measure atmospheric pressure using mercury, water or air. ... If a high pressure system is coming, you can expect clear skies and cooler temperatures.

What does a barometer measure?

A barometer is a scientific instrument used to measure atmospheric pressure, also called barometric pressure. ... Atmospheric pressure is an indicator of weather. Changes in the atmosphere, including changes in air pressure, affect the weather. Meteorologists use barometers to predict short-term changes in the weather.

Is barometric pressure related to temperature?

Air pressure depends on the temperature of the air and the density of the air molecules. ... For example, if air pressure increases, the temperature must increase. If air pressure decreases, the temperature decreases. It also explains why air gets colder at higher altitudes, where pressure is lower.