Final answer:
METARs in the U.S. begin with the letter K followed by a three-letter code specific to the airport.
Step-by-step explanation:
METARs are aviation weather reports that provide information about current weather conditions at an airport. They have a four-letter identifier called an ICAO code, which is assigned to each airport. In the United States, METARs begin with the letter K followed by a three-letter code specific to the airport. For example, KATL is the METAR code for Hartsfield-Jackson Atlanta International Airport.