Yes, PRECIPITATIONS is a Scrabble word!

Letter values in Scrabble US: P 3, R 1, E 1, C 3, I 1, P 3, I 1, T 1, A 1, T 1, I 1, O 1, N 1, S 1.

Is it a valid word?

PRECIPITATIONS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

the quantity of water falling to earth at a specific place within a specified period of time
the process of forming a chemical precipitate
the falling to earth of any form of water (rain or snow or hail or sleet or mist)
the act of casting down or falling headlong from a height
an unexpected acceleration or hastening
overly eager speed (and possible carelessness)