What does "BKN040" signify in a METAR?

"BKN040" in a METAR report indicates broken clouds at an altitude of 4,000 feet above ground level. The abbreviation "BKN" specifically refers to broken cloud cover, which signifies that between 5/8 and 7/8 of the sky is covered by clouds. The number "040" denotes the height of these clouds above the surface, measured in hundreds of feet. Therefore, "040" translates to an altitude of 4,000 feet. Understanding this information is crucial for pilots and air traffic controllers, as cloud cover can significantly affect flight operations and weather conditions at an airport.

The other options do not accurately describe the meaning of "BKN040." The term does not refer to cloud cover percentages or visibility and does not pertain to broken clouds at a lower altitude of 400 feet, which would require a different designation.