If the sky is cloudless, there are no clouds in it.
英汉词典释义
adj.
无云的,晴朗的
The sky is quite blue and cloudless.蔚蓝的天空晴朗无云。The sun shone on for hours in a cloudless sky.天放晴了几个小时。It was the first of August,a perfect day,with a burning sun and a cloudless sky.八月一日这天,阳光普照,万里无云。