isoneph

noun

1. An isoline indicating equal cloud cover.

   “After plotting the amounts in oktas, isonephs were drawn at two-okta intervals. Closely spaced isonephs indicate a sharp edge to a cloud sheet, the edge approximately coinciding with the four-okta isoneph. A station reporting four oktas and lying in a region of close isonephs would have one side of its sky relatively cloudfree and the opposite side covered.”