How is 5/8 of the sky covered by clouds at 10,000 feet AGL encoded in column 10?

The correct encoding for 5/8 of the sky covered by clouds at 10,000 feet Above Ground Level (AGL) is represented as "BKN100." In aviation weather reporting, the term "BKN" stands for broken clouds, which indicates that between 5/8 and 7/8 of the sky is covered by clouds. Since 5/8 fits within this definition, BKN is the appropriate term to use.

The altitude "100" signifies that the cloud base is at 10,000 feet AGL. Overall, "BKN100" clearly communicates both the extent of cloud coverage and the altitude of the clouds.

SCT100, which stands for scattered clouds at the same altitude, would not accurately reflect the 5/8 coverage, as "scattered" typically indicates less than 5/8 cloud cover. OVC100 indicates overcast conditions, meaning clouds cover the sky completely, which is not the case here. CLR100 signifies clear skies with no significant cloud cover, which again does not correspond to the 5/8 coverage described in the question.