H = Height of the lowest cloud base
CM = Type of middle cloud
CH = Type of high cloud
WWWW = Two digit code representing the site’s current weather. Some codes refer to weather during the previous hour, but not at the time of the observation. The code with the highest priority should appear first. If only one WW group is applicable, use that code twice.
Here are a couple examples of cloud weather codes:
6 = 6 oktas of clouds
5 = Stratocu not formed by the spreading out of cu
7 = Cloud base between 5000 and 6500 feet
0 = No mid cloud
8 = Cirrostratus (not covering and not invading the sky)
20 = Drizzle during the previous hour, but not at the time of ob
01 = Clouds generally dissolving or becoming less developed during past hour.
The code for a clear sky would be: