The weight of the entire column of air above a point produces barometric pressure. It is the same quantity measured by a barometer and reported in weather observations. Values change with altitude, temperature, and the movement of weather systems.

Standard sea-level pressure is about 1013.25 millibars. Mountains experience lower values simply because less air sits above them. Weather maps reduce all readings to sea level so patterns stand out clearly.

Rapid drops in barometric pressure often precede storms. Steady rises usually accompany clearing skies. Pilots use pressure settings to keep altimeters accurate. Even small daily variations of a few millibars are routine and expected.

Tracking these numbers remains one of the oldest and most reliable tools in meteorology.