What is the first letter of the four-letter identifier for METARs in the U.S.?

The correct answer is C, which relates to the four-letter identifier for METARs (Meteorological Aerodrome Reports) in the U.S. METARs are aviation weather reports that provide essential information about current weather conditions at airports.

In the United States, these reports utilize a specific format for their identifiers, which begin with the letter 'K'. This letter signifies that the station is located in the U.S. and follows the convention set by the International Civil Aviation Organization (ICAO), where the first letter indicates the country. In this case, the 'K' is used as a prefix for reporting stations in the mainland U.S., followed by three letters representing the specific airport.

Understanding this format is crucial for pilots and others who rely on METARs for accurate and timely weather information. Recognizing that all U.S. reporting stations follow this 'K' convention can help pilots effectively interpret weather conditions when planning flights.