What does "BKN000" signify in a METAR report?

In a METAR report, "BKN000" indicates "broken clouds at zero feet." This serves as a crucial marker for air traffic controllers and pilots as it denotes a significant weather condition involving the cloud ceiling. The term "broken" refers to an amount of cloud cover that is significant but not complete, specifically between 5/8 and 7/8 of the sky covered by clouds. The "000" indicates that this cloud cover is present at ground level, or very low, which can pose particular challenges for flight operations, especially for takeoff and landing.

Understanding this significance is vital for operational safety, as it informs flight crews of the current ceiling height and helps in making informed decisions regarding visibility and approach procedures. Other interpretations of cloud conditions are critical too, and assessments such as total cloud cover or visibility thresholds are important in different contexts, but "BKN000" specifically highlights the presence of broken cloud cover at an extremely low altitude, indicating an obstruction to visual flight rules adherence in that location.