Negation, Long and Short Form
I want to say "The weather is not cold"

Which of these do I use?

날씨가 못 추워요 / 날씨가 추위지 얺아요 / 날씨가 안 추워요.

If you could explain why, I would be grateful.

Question

Negation, Long and Short Form
I want to say "The weather is not cold"

Which of these do I use?

날씨가 못 추워요 /  날씨가 추위지 얺아요 / 날씨가 안 추워요.

If you could explain why, I would be grateful.

Answer

The third one, 
but the long form of negation would be more natural like "날씨가 춥지 않아요."

e.g. 
to be cold = 춥다 / to be hot = 덥다
The long form(neutral) ☞ 춥 + 지 않아요 / 덥 + 지 않아요
The short form(emphasized) ☞ 안 + 추워요 / 안 + 더워요

\^o^/