What does QNH mean on a METAR report?

QNH on a METAR report refers specifically to the current altimeter setting in use, which is critical for pilots and aviation operations. It indicates the atmospheric pressure at sea level, measured in inches of mercury or in hPa (hectopascals), which is used to calibrate altimeters before takeoff and landing to ensure accurate altitude readings.

When the QNH is set correctly, it helps to ensure that an aircraft's altitude readings are accurate throughout its journey, helping to maintain safe separation between aircraft and obstacles on the ground. The importance of accurately setting and understanding QNH cannot be overstated as it directly affects flight safety.

The mention of "the lowest altimeter setting expected at this time" misunderstands the definition of QNH. While weather conditions can indeed lead to varying altimeter settings, QNH specifically represents the current atmospheric pressure rather than a forecast or expected pressure. This distinction is vital in understanding how aeronautical terms relate to operational safety.