What are you talking about ? If it was warmer then the shepherds definitely would be out in the fields. That’s the whole point. That the shepherds were out in the fields.
I dont really understand why people try so hard to figure out or argue about the date Christ was born. If it was important and God wanted us to know the date he would have revealed it in his word.
Just think how much time and energy is wasted on this subject when everyone could be speaking of things that have an impact on our salvation.