Which of the following is NOT a basic element of a METAR?

The correct choice identifies humidity as not being a basic element included in a METAR report. METAR, which stands for Meteorological Aerodrome Report, provides essential weather information necessary for pilots and air traffic control, primarily focusing on the conditions that directly affect aviation safety.

The fundamental elements of a METAR include the type of report, visibility, clouds, wind direction and speed, temperature, dew point, altimeter settings, and significant weather phenomena. Humidity, while important for understanding overall weather conditions, is not directly reported in METARs. Instead, it can be inferred from temperature and dew point values.

The other elements listed, such as type (indicating whether the report is routine or special), visibility (crucial for pilots to ascertain flight safety), and altimeter (which provides vital pressure information for altitude calculations), are all core components of a METAR, reinforcing their essential role in aviation meteorology.