A falling barometer reading usually indicates that a storm or wet weather is approaching. A more rapid change indicates the weather will change sooner. A barometer reading that remains steady indicates that no immediate change in weather should be expected.
Approaching low-pressure systems or fronts will often bring precipitation and clouds. Barometric pressure readings and the change in atmospheric pressure over time, known as pressure tendency, have been used to forecast weather since the late 1800s. The changes in atmospheric pressure are caused by differences in air temperature above the Earth's surface. These changes cause both wind and pressure patterns to develop. Air temperature changes can be caused by wind moving air over various land masses, such as mountains, and water bodies, such as oceans.