In Seoul, January typically marks the coldest month of the year, with average temperatures ranging from -5°C to -1°C (23°F to 30°F).

However, temperatures can dip even further during cold spells, sometimes reaching as low as -10°C to -15°C (14°F to 5°F), especially during the night or early morning. Snowfall is also common in January, although it's usually light to moderate, and snowstorms are relatively rare.

Humidity is low, but the wind chill can make it feel even colder than the air temperature suggests. It's also a dry month, with average rainfall being quite minimal.

So, you can expect cold, crisp weather, sometimes with snow, and if you're planning to visit, layering up with warm clothes, including a good winter coat, gloves, and a scarf, is a must.