(covers information from several alternate timelines)
Rain on Ferenginar
Rain on Banea
Rain is precipitation of liquid from the atmosphere which falls to the ground. It is caused by condensation of the liquid when the humidity passes the saturation point of the air it is in.
On most class M planets, rain is in the form of liquid water. On class M planets nucleogenic particles are necessary to produce rain; without them a planet would be incapable of producing any rain at all. Some forms of technology are capable of destroying nucleogenic particles. The Caretaker's race caused this damage to the Ocampan atmosphere, and as such it had no rain. (VOY: "Caretaker")
Ferenginar was well known for its near-constant rain. Because of the extremely rainy climate of their homeworld, the Ferengi had 178 different words for rain in all its various forms. They also had no word for "crisp," as all food on Ferenginar became soggy very quickly. (DS9: "Let He Who Is Without Sin...", "Family Business", "The Magnificent Ferengi", "Valiant") In 2375, an accident at a power plant there produced toxic rain. (DS9: "The Dogs of War")
On Banea, in the Delta Quadrant, rain storms were called "cloudbursts." (VOY: "Ex Post Facto")
Many planets, such as Caldos and Risa, had weather modification networks which, among other things, controlled rainfall. (TNG: "Sub Rosa"; DS9: "Let He Who Is Without Sin...")
In 2373, Michael Eddington lamented the lack of rain and too much of it on a planet in the Demilitarized Zone. (DS9: "Blaze of Glory")
In an alternate timeline in which Benjamin Sisko suffered temporal displacement, Melanie visited Jake Sisko on a particularly rainy night in 25th century New Orleans. (DS9: "The Visitor")