The weight of clouds can reach quite astonishing proportions. For example, a cumulonimbus cloud, commonly known as the thunder cloud, can contain up to 300,000 tons of water. The fact that a mass of 300,000 tons of water can remain aloft is amazing.
Attention is drawn to the weight of clouds in the Qur'an: It is He Who sends out the winds, bringing advance news of His mercy, so that when they have lifted up the heavy clouds... (7:57) ...it is He Who heaps up the heavy clouds. (13:12)
For hundreds of years it was impossible to have any information about the weight of clouds. This information, revealed in the Qur'an, but discovered only recently, is yet another proof that the Qur'an is the Word of Allah.