Ibn Umar RA narrated that the Prophet (Sallallahu Alayhi Wa Sallam) said, "The keys of the Ghayb (Unseen) are five and no one but Allah the Almighty knows them: (1) No one knows what will happen tomorrow but Allah; (2) No one knows by how much the wombs fall short (of their time) but Allah;(3) No one knows when it will rain but Allah; (4) No human soul knows in what land it will die; (5) No one knows when the Hour will be but Allah." [AHMED]
These five issues of the absolute Ghayb (Unseen) explains volumes and to emphasize how only Allah, the Omniscient, knows their absolute realities. That is why the author here shall confine his argument to the third case, "No one knows when it rains but Allah."
Rain is one of man's provisions on earth, which is only provided by Allah. Sometimes rain also comes as a punishment, and it is only Allah who sends punishment on humankind. Moreover, the fall of rain is a very complicated process that involves many factors over which man has no control. Several physical and chemical reactions, which are not fully perceived, are involved in the process of rainfall.
Of these reactions are the trade winds, the evaporation of water from surface water (e.g. lakes, streams, oceans, etc.) – and the air masses that gather moisture when passing over warm bodies of water or wet land surfaces and all living organisms. The moisture or vapor is carried upward into the air mass by turbulence and convection. As water vapor rises, the temperature of the air cools and the vapor eventually condenses on particles suspended in the air. These water droplets are gathered together by air, to form clouds, which are again driven by the wind. The wind keeps generating more clouds, joining them together, moving and spreading them out across the sky. Sometimes the wind generates different types of clouds, by driving these rain clouds to accumulate into a heap of layers that keeps forming to reach the uppermost layer of the atmosphere.
Wind keeps driving more water vapor and dust particles (acting as nuclei for vapor condensation) into these clouds, which make moisture droplets grow bigger and bigger until they reach the size suitable for the precipitation in the form of rain, hail or snow. All these reactions take place while clouds are in continuous motion; no one except for Allah the Almighty knows the time, place and the amount of rain it will release.
Of the factors affecting this complicated process is the amount and type of electric charges in an individual cloud or in colliding clouds, and the effect of the solar wind – The solar wind is a continuous stream of ions (electrically charged particles) that are given off by the sun. The source of the solar wind is the Sun's hot corona – on the earth's atmosphere, in addition to other factors, which may or may not be known to us.
Moreover, clouds do not carry at any one time more than 2% of the water vapor present in the atmosphere, which is estimated to be 15,000 sq. km. Water droplets, which these clouds carry, are extremely small in size that they hardly exceed 0.001 mm in diameter. Due to their high viscosity, these tiny droplets stick to the air particles; that is why they do not precipitate in the fonn of rain unless they are provided with more water vapor or dust particles, which are blown by the wind from the surface of the earth, thus helping in the process of water release (from the clouds) by Allah's Will.
This may also take place through joining clouds together, even though they may be different in their temperature, humidity, electric charges and other characteristics. This clearly shows how the process of rainfall is really a secret of this universe that cannot be reached or arranged by any one except for Allih the Almighty. Scientists exert much effort to understand how rain is formed and precipitated from various clouds carrying water vapor and particles, however, it is still a process beyond man's ability no matter how advanced and developed his knowledge and technology are.
This became evident in recent years, when meteorologists attempted to develop effective methods of artificial precipitation through spraying clouds with chemicals, which have a great affinity for water. In spite of the success of these attempts, scientists could not control the areas of the precipitation of rainwater, emphasizing what the Prophet (Sallallahu Alayhi Wa Sallam) meant when he said, "No one know when it rains but Allah."
Moreover, in weather forecasts, rainfall predictions are made only a few hours/weeks/months before rainfall actually takes place, and in many cases, they are not reliable.
Glorified be Allah, the Almighty who taught this knowledge to the last of His Prophets and Messengers, Muhammad (Sallallahu Alayhi Wa Sallam), who in turn conveyed it in extremely accurate scientific language to be lasting evidence on His divine Message.