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From December to March, fine particle levels average about 45 per cent higher than in the other eight months, on the government’s own figures. Those four months are Korea’s designated fine dust season. Seoul’s nights also average below freezing in all three winter months.
Cold, by month
Averages for Seoul from the Korea Meteorological Administration, over the thirty years to 2020.
| Average high | Average | Average low | Rainfall | Wet or snowy days | |
|---|---|---|---|---|---|
| December | 4.2°C / 40°F | 0.2°C / 32°F | -3.4°C / 26°F | 22.6mm | 7.8 |
| January | 2.1°C / 36°F | -2.0°C / 28°F | -5.5°C / 22°F | 16.8mm | 6.1 |
| February | 5.1°C / 41°F | 0.7°C / 33°F | -3.2°C / 26°F | 28.2mm | 5.8 |
January is the coldest. Its average temperature is the only one below zero, and it has the lowest rainfall of the three. Expect it cold and dry.
By every temperature column February is the mildest, and rain or snow comes on fewer days than in the other two.
For warmth, December sits between them. It also has the most wet or snowy days.
A January day runs from -5.5°C at dawn to 2.1°C in the afternoon. That calls for a coat that works at both ends, with layers under it you can open. For what a heated-floor room is like to sleep in, see the Seoul neighbourhood guide.
Seoul’s coldest reading since records began in 1907 was -23.1°C on 31 December 1927. That was a one-off record, not a winter to plan for.
The air
Forecasts come in four grades, taken from whichever of two particle sizes reads worse.
| Grade | PM2.5 | PM10 |
|---|---|---|
| Good | 0 to 15 | 0 to 30 |
| Moderate | 16 to 35 | 31 to 80 |
| Bad | 36 to 75 | 81 to 150 |
| Very bad | 76 and above | 151 and above |
Korean forecasts give the grade name. An app from home is more likely to show a raw number, and the table converts one into the other.
Official advice is short. Look at the forecast on Air Korea before committing to a day outdoors. And if you want a mask, the grades to look for are KF80, KF94 and KF99, certified by the Ministry of Food and Drug Safety. On Bad and Very bad days the general public is advised to limit long or strenuous outdoor activity. Children, older people and anyone with a lung condition are advised to stay indoors where they can on Very bad days.
Short days
| Sunrise | Sunset | |
|---|---|---|
| 21 December | 7.41am | 5.18pm |
| 15 January | 7.44am | 5.38pm |
| 28 February | 7.04am | 6.25pm |
On the shortest day there are under ten hours of light. Sunset gains more than an hour by the end of February, while sunrise still sits around twenty to eight in mid-January. Afternoons come back before mornings do. Outdoor plans fit best around noon.
Skating and skiing
Seoul City sets up a skating rink in Seoul Plaza each winter and posts the dates on its plaza news page. The 2025 to 2026 season ran from 19 December to 8 February, the one before on a similar pattern, with the announcement coming in December. A January trip fell inside both of those seasons, and an early December one did not. No date for 2026 to 2027 has been given yet.
Resorts within reach of Seoul each announce their own opening, so there is no single ski season to quote. Each resort’s own page is the place to look.
Gyeongbokgung’s recent night viewings have run once in spring and once in autumn, with no winter dates announced. The autumn guide gives the most recent dates.
Lunar New Year 2027
Seollal falls on Sunday 7 February 2027. The holiday runs from Saturday 6 to Tuesday 9 February, four days, with the Tuesday added as a substitute because the day itself lands on a Sunday.
Some sites give the date as 6 February. Korea’s official almanac says the 7th. With four days off across the country, book trains and intercity buses for those dates as early as the operators allow. The KTX guide covers when seats open and what to do if a train sells out.