Winter comes early to northern Korea, usually beginning in October when the intense arctic cold of the Siberian High begins to move into northern Korea. The northern rivers begin to freeze over as severe cold waves sweep south across the Manchurian Plain, bringing frigid, dry air into Korea. For most of Korea the real cold comes later, around January. Although precipitation in December is slight, cyclonic storms can drag enough snowfall onshore to cover the ground across most of North Korea.
Winter in Korea can last up to six months in the northern part of the peninsula, but generally lasts only three months in central and southern Korea. Temperatures average below freezing during the months of December, January, and February, except for the southern coastal areas.
January is the coldest month in Korea. The average January temperature in Chongjin, near the Chongjin Reservoir, is just -8°C (16°F). January in Seoul averages a chilly, -5°C (21 F). At Sinuiju, near the mouth of the Yalu River, and at Taegu in southern Korea the average temperature is only -5°C (23°F). The port city of Pusan fares little better, with January temperatures averaging only -1°C (30°F). Considering these are only average temperatures based on the past 17 to 20 years, temperatures can, and have been much colder. The lowest temperature recorded at Chongjin in the past 20 years was a bone-chilling -21°C (-7°F).