When transitioning from low pressure to higher pressure, how is the altimeter affected?

When transitioning from low pressure to higher pressure, the altimeter indicates a lower altitude than the actual altitude. This occurs because an altimeter measures altitude based on the atmospheric pressure and compares it to a standard setting (usually set to 29.92 inches of mercury, or Hg).

In low-pressure systems, the air pressure is lower than the standard, causing the instrument to read higher altitudes. However, as aircraft move to an area of higher pressure, if the altimeter is not adjusted to the new local altimeter setting, it will continue to indicate the altitude as if it were still in low pressure. Consequently, the aircraft is actually at a lower altitude than what the altimeter displays, leading to the scenario where it shows a lower altitude than the aircraft’s true position.

Understanding this relationship between pressure changes and altimeter readings is crucial for pilots to maintain accurate altitude awareness and flight safety.