I advise to read chapter 15, Invoking Allah for Rain (Istisqaa), of Sahih Bukhari (collection golf Hadith, sayings, of prophet Mohamed peace be upon him).
13:12 Ar-Ra'd
هُوَ الَّذِي يُرِيكُمُ الْبَرْقَ خَوْفًا وَطَمَعًا وَيُنْشِئُ السَّحَابَ الثِّقَالَ
It is He (God) who shows you lightening, [causing] fear and aspiration, and generates the heavy clouds.