If a flight is made from high pressure into low pressure without adjusting the altimeter, what will the altimeter indicate?

When a flight is conducted from an area of high pressure to an area of low pressure without adjusting the altimeter, the instrument will indicate a higher altitude than the actual altitude. This occurs because the altimeter is calibrated based on the pressure setting at sea level (known as the altimeter setting). When flying from a high-pressure area (where the air is denser) to a low-pressure area (where the air is less dense), the altimeter does not automatically adjust its reading, which results in an incorrect indication.

As the aircraft ascends into lower pressure air without recalibrating, the altimeter relies on the unchanged pressure reference. Since the actual air pressure is lower than what the altimeter was set for, it interprets the aircraft as being at a higher altitude than it truly is. Understanding this concept is crucial for pilots, as operating with an inaccurate altitude reading could lead to severe consequences, particularly in relation to terrain clearance and maintaining safe vertical separation from other aircraft.