Temperatures across the nation plummeted Tuesday as a frigid air mass descended from the north, with the cold snap expected to persist this week, the weather agency said. Morning temperatures fell to minus 11.8 degrees Celsius in Seoul, minus 12.8 Celsius in the western port city of Incheon, minus 21.2 Celsius in the eastern coastal county of Yanggu and minus 2 Celsius in the southeastern port city of Busan, according to the Korea Meteorological Administration. Daily highs are expected to reach minus 4 to plus 7 Celsius, with day temperatures in many parts of the nation forecast to remain below 0 Celsius. The cold spell is expected to continue until at least the weekend, with the morning lows reaching minus 17 to minus 4 Celsius on Wednesday. Meanwhile, some eastern coastal areas will see light snowfall of less than 1 centimeter Tuesday morning. Snowfall is also expected late at night in some coastal parts of the central province of South Chungcheong and the southwestern provinces of Jeolla, as well as the southern resort island of Jeju. Southwestern coastal areas, Jeju Island and the east