I never close the pop hole to my coop as I have a very secure run.
My chickens hate the snow. HATE IT! Fortunately, as my coop is raised off the ground, they can pop out and scratch in the snow free dirt under the coop at will.
I think how much bad winter weather the hens can stand depends on breed. My speckled sussex will be outside, no matter how cold, as long as it isn't windy. We have had days where the high was 5 degrees, and they will be under the coop, clucking and crawing at me when I go outside to look for eggs. (They love me!)
The silkie mix and the easter eggers all prefer to stay inside when it is frigid, but if it gets into the teens or 20's, they go out too.
When I get chicks in the spring I will be getting only cold hardy breeds as I have seen how well these speckled sussex due in our cold winters. Since I have no choice in the weather, I may as well have chickens that act like they are not bothered.