The conditions associated with air of continental polar origin, often dominated by an anticyclone behind a cold front, that moves south into central and eastern parts of the USA. Cold waves are defined as a fall of 11 °C or more to a minimum base (−18 °C in northern, central, and northeastern regions) within a 24-hour period. In southern states (Florida, California, and the Gulf Coast) the minimum fall is 9 °C and the base minimum 0 °C.