Definitions for "PARTLY CLOUDY"
The character of the day’s weather when the average cloudiness, as determined from frequent observations, has been from 0.4 to 0.7 for the 24hr period. In popular usage, when clouds are conspicuously present, but do not completely dull the day of the sky at any moment. Think of partly cloudy as the total cloud cover being one slice of a pie, and the sunshine constituting the remainder of the pie.
When the predominant/average sky condition is covered 3/8 to 4/8 with opaque (not transparent) clouds. Same as Partly Sunny.
the appearance of the sky when 3/10ths to 6/10ths of the sky is covered with clouds.