What unit of measurement is used to describe cloud base heights in a METAR?

The correct unit of measurement used to describe cloud base heights in a METAR report is expressed in hundreds of feet above ground level (AGL). This means that if a METAR indicates a cloud base at a height of, for example, "04," it would be interpreted as 400 feet AGL. This standardized method allows for concise reporting of cloud heights, making it easier for pilots and meteorologists to assess weather conditions quickly.

Understanding this format is crucial for interpreting METARs accurately, especially in aviation, where knowing the cloud base is vital for flight safety and operations. The other options do not align with the conventional reporting standard used in METARs. Meters and feet AGL are not the correct format, as they do not reflect the way cloud bases are typically recorded in meteorological reports. Additionally, representing cloud heights in thousands of feet is uncommon and can lead to misunderstanding of altitude. Using hundreds of feet AGL provides a clear and specific detail that is essential for flight planning and safety assessments.