How is 5/8 of the sky covered by clouds at 10k feet AGL encoded in column 10?

The correct answer is based on the definition of cloud coverage in meteorological terms. When 5/8 of the sky is covered by clouds, this is classified as broken clouds. In aviation weather reporting, broken cloud coverage is indicated by "BKN," followed by the altitude of the cloud base in hundreds of feet.

Since the question specifies that the cloud cover occurs at 10,000 feet above ground level (AGL), the encoding includes "100" to signify this altitude (10,000 feet divided by 100). Therefore, "BKN100" accurately represents that there are broken clouds at this specific altitude.

The other options denote different cloud coverage or are not accurate representations of the situation described. "OVC" stands for overcast, indicating that 8/8 of the sky is covered; "SCT" refers to scattered clouds, denoting that 1/8 to 4/8 of the sky is covered, which does not match the 5/8 coverage specified; "CLR" indicates clear sky, showing no significant cloud cover at all. These distinctions highlight why "BKN100" is the correct encoding for reporting 5/8 cloud coverage at 10,000 feet.