[Ng Jing Kiat]

Ng Jing Kiat asked the Naked Scientists:
   
Hi there Naked Scientists I've got a question for you:

Why are there usually more clouds in the evening, where you can't see the sky clearly as compared to day?

Thanks! Keep up the good work.

What do you think?

[CliffordK]

The water vapor capacity of air, or maximum humidity varies with temperature.

The hotter the air, the more moisture that it can hold.

As the temperature is reduced, it will drive the moisture out of the air in the form of dew, fog, or clouds. 

Thus, clouds may form in the evenings as temperatures fall, and fog can "burn off" by mid-morning.