Just keep the air on recirculate, and the vents pointed at the windows. I've never had serious fogging problems with the Impreza in any season. The key is to keep the windshield as warm or warmer than the outside air. This will keep condensation off the window. The only fog problems I've had are in the summer when I have the AC blowing on the windows (I don't like it in my face) and some frost builds up at the base of the windshield.