Radak: They are clouds. They are called Nesi'im because they rise from the land and are elevated above - "v'Ed Ya'aleh Min ha'Aretz" (Bereishis 2:6).

Malbim: They are vapors. They rise to the place of the clouds and the evaporation cycle. The vapors are full of wind and air; they are hidden from the eye.

Radak: From the end of the dry land, i.e. the sea. Clouds rise from there - "ha'Korei l'Mei ha'Yam va'Yishpechem Al Pnei ha'Aretz" (Amos 5:8). We find that Eliyahu told his youth "Habet Derech Yam", "Hine Av Ketanah k'Chaf Ish Olah mi'Yam" (Melachim I, 18:43-4).

Rashi: This is lightning, which illuminates before rain.

Radak: This is a great wonder He makes lightning with rain. The lightning is fire and the water does not extinguish the fire.

Malbim: The element of fire in the Nesi'im spreads them out. When Hashem wants rain to fall, He separates the element of fire and electricity from them, and lightning comes into being. Via this He takes out the element of Ru'ach from its storehouses (it is stored in the vapors), and via this there is rain.

Rashi: It is an expression of Metzi'ah (a found item). I.e. he prepared storehouses for wind, and they are available for him to send on his mission.

Radak: This is like Motzi. The wind pushes the rain to the corner to which it goes. Before it blows, it is not felt. Now that it blows, it is as if He took it out.

Radak: Three of the four 'elements' appear to the eye (earth, fire and water), but wind is not seen; it is like a matter hidden in a storehouse.

Radak citing Ibn Ezra: Ru'ach is potential; it is stored.

Malbim: Refer to 135:7:3:3.