This was a thunderbolt out of a clear sky.

这是晴天霹雳。

youdao

The news was like a thunderbolt out of a clear sky.

这消息犹如晴天霹雳。

《新英汉大辞典》

And beyond that great woolly clouds floated almost motionless in a clear sky.

再往上看就是一片清澈的天空，大朵大朵羊毛般的云团一动不动地吊在上面。

youdao

And one day, outof the blue clear sky, I got a letter from Jenny wondering if I couldcome down to Savannah and see her, and that'swhat I'm doing here.

VOA: standard.other

The sky was just a little lighter blue than his suit, clear and even with only one cloud in it, a large, blinding white one with curls and a beard." Notice that image of the cloud, the blinding white cloud.

天空比他身上蓝色的西装颜色更亮，更清朗，甚至,空中只有一朵白云，是大而亮白的螺旋状和,胡须状，注意这多云的图像，一朵亮白的云。

耶鲁公开课 - 1945年后的美国小说课程节选

It was a day like this one -- a clear blue sky, but a sky that would soon be filled with clouds of smoke and prayers of a nation shaken to its core.

WHITEHOUSE: President Obama Speaks at a Pentagon Memorial Service in Remembrance of 9/11 | The White House

Twenty-four hours ahead of the storm, under a perfectly clear sky, my airline canceled my flight from DC to NYC.

FORBES: The Only Thing Right About a Forecast Is That It's Wrong

You know that feeling on a clear blue sky day.

FORBES: The Data Smog That Envelops Us All