I was out in the little dome in the cold a couple nights ago. I had a pet heating pad going on the small table with the ep case sitting on it. The pad only gets to about 100F before it turns off. I couldn't focus the scope precisely. I turned off the pad and things improved greatly. The heat plume from the pad was exiting the dome slit in front of the objective. The same thing happens with body heat. Bundling up sufficiently helps the body heat to not escape and ruin the seeing.
This problem is as old as observatory domes. Some domes are much more susceptible to it than others. A wide dome slit helps tremendously. My old mentor Per Darnell told me that the old observatory in Copenhagen on Østervold had a relatively narrow dome slit and more than two persons in the dome caused bad seeing, despite the dome being quite large.
I think the professionals call it "dome seeing" or "slit seeing". It's one of the downsides of a dome, compared to a roll-off roof observatory.