بسم الله الرحمن الرحيم
See you not that Allâh drives the clouds gently, then joins them together, then makes them into a heap of layers, and you see the rain comes forth from between them. And He sends down from the sky hail (like) mountains, (or there are in the heaven mountains of hail from where He sends down hail), and strike therewith whom He wills, and averts it from whom He wills. The vivid flash of its (clouds) lightning nearly blinds the sight. [Tafsir At-Tabarî].