1)
What is the significance of a cloud blocking our prayers?
1.
Brachos 32b: Rava would not decree a fast on a cloudy day 1 (because the prayers would not be accepted easily).
2.
Rav Sadya Gaon: You covered with a cloud, as if our Tefilah cannot pass to you.
3.
Ibn Ezra: This is a Mashal, as if the cloud divides between Tefilah and Hashem.
1
This implies that a cloud truly blocks prayer. (PF)