Addition to ShyTorque's good pointers on misting...... if it gets reeeeeeeeal cold, the problem becomes frosting. Even though the air is dry, the surface temperature of the windows can be -30 or -40º. The moisture from all those heavy breathing pax sticks hard, and at those temperatures, without windshield heat, can take forever to get rid of. As ShyQ says, leave the doors open (Brrrr), or start before loading pax and run the heater/defrost.