[The Thick Clouds]

He made darkness His hiding place,

His pavilion round about Him -

darkness of water, thick clouds of the skies.

(Tehillim 18:12)

Darkness of waters means an accumulation of clouds; thick clouds of the skies means clouds that cover the sky.  "He made darkness His hiding place" alludes to the profound difficulty of knowing G-d, just as it is impossible to know what is inside a dark place.  For our material aspect keeps us separated from knowing the Almighty, but never despair, because G-d is always present, even when we can't see Him.
[MeAm Lo'ez, Perek Shira]