In aviation, this term refers to the lowest altitude, expressed above ground level (AGL) or mean sea level (MSL), reported as either broken or overcast. This critical weather parameter signifies the height at which at least more than half of the sky is obscured by clouds, effectively limiting visibility for pilots. For example, if a weather report indicates a reading of 3,000 feet, it denotes that more than half of the sky is covered by clouds at that altitude.
This meteorological information is vital for flight planning and safety. It dictates whether visual flight rules (VFR) or instrument flight rules (IFR) must be followed. Low readings can necessitate instrument approaches or even prevent takeoffs and landings altogether. Historically, accurate determination of this value has been a key focus of aviation meteorology, with advancements in weather observation technology continually improving the precision of reported heights.
