snow in the coop - too cold for polish?

I'm in northern Michigan and right now we are under blizzard warnings. Earlier in the year I winterized my coop and eliminated the drafty areas. However I didn't do a great job on the east side. I left the eaves open for ventilation and the top of the peak again on the east side. Most of our winds come from the south or west. However this blizzard that we are dealing with now is blowing from the east. So this morning I had to shovel snow from the coop. I stuffed some old sheets into the eaves until the wind direction changes. All I have for heat is a light above their roosts. How do I determine if they are warm enough? What behavior shows they are too cold? I have mainly polish that I am worried about although I am concerned about my guineas also. I know I'm going to have a moisture problem once it warms up a little.