“It’s too cold to snow!” How often have you heard that complaint? The truth is that it doesn’t get too cold to snow – it gets too dry to snow! As with any precipitation event, condensation has to occur at a greater rate than evaporation for moisture to fall. When that happens, regardless of the temperature, you will see precipitation. The fact behind the too-cold-to snow myth is that cold arctic air masses tend to be very dry. So when an arctic air mass moves south, it brings those cold temperatures but it’s unlikely to have condensation rates high enough to produce snow. That can change if it meets a source of moisture, such as moist air moving up from the Gulf of Mexico. So remember, it isn’t the cold, it’s the moisture.
Mary Knapp, Weather Data Library