How is "indicated altitude" affected by atmospheric conditions?

Indicated altitude is the altitude read directly from the altimeter when it is set to the local atmospheric pressure. This reading can be influenced by changes in atmospheric pressure. When the atmospheric pressure decreases, as it typically does in lower pressure conditions (such as when flying in a low-pressure system or at higher altitudes), the altimeter will indicate a higher altitude than the actual elevation above sea level. This is due to the altimeter being calibrated to a standard pressure of 29.92 inches of mercury (Hg). If the local pressure is lower than this standard value, the altimeter will interpret the decreased pressure as being at a higher altitude.

Understanding this relationship is crucial for pilots, as relying solely on indicated altitude without adjusting for atmospheric pressure could lead to a dangerous situation, such as flying at a lower altitude than intended in a low-pressure environment. Therefore, indicated altitude indeed rises in lower pressure conditions.