Unless + not
I will not go for a walk unless it’s not warm weather

Is it possible to use unless with not?

Question

Unless + not
I will not go for a walk unless it’s not warm weather

Is it possible to use unless with not?

Answer

How to use unless + not 
I will not go unless you pay for my ticket.
He will not talk to me unless I call him.
Your sentence sounds better written:
I will not go for a walk unless it’s cool (outside).

Answer

It means "I won't go if it's warm". The guy is a cold weather-lover)