Fire, air, water and earth are not fixed substances but change into each other, because each is potentially present in the others. They sit in nested layers by weight: earth at the centre, then water, then air, then fire at the top. Weather happens where these layers mix and transform.
Heat draws vapour up from water. How high it rises depends on how much heat there is compared with how much water. Dew and frost form only on clear, still nights: a clear sky lets the vapour rise during the day, and the lack of wind lets it settle and condense.
When seawater is heated, what rises off it and is caught again is fresh water. The salt stays in what is left. Sailors used this, boiling seawater and catching the vapour in sponges to get water they could drink.
A whirlwind is a strong wind that cannot break free of its cloud. The resistance turns its push into a spinning eddy, which comes down to the ground dragging the cloud with it. Thunderbolts work in a similar way: thin, dry vapour is squeezed out of a cloud.
Given endless time, places that are sea now were once land, and land now will one day be sea. Rivers themselves are not permanent: their sources were once dry and will dry again. Change too slow to see in a lifetime still reshapes the earth completely.