Yes, KATABATIC is a Scrabble word!

Letter values in Scrabble US: K 5, A 1, T 1, A 1, B 3, A 1, T 1, I 1, C 3.

Is it a valid word?

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

of an air current or wind; moving downward or down a slope because of cooling especially at night

Not playable in Scrabble US: CATABATIC.