Like many popular destinations in Asia, Seoul can be very hot and humid in the summers and cold in the winters. Rainy season starts in July and extends through August, thereby making the spring and fall the most pleasant times of year.
For travelers headed to Seoul, the summer months between June and August make up the busiest season, as well as Korean New Year in February and Korean Thanksgiving in August. Both holidays follow the lunar calendar, so exact dates will shift from year to year. Since these holidays place heavy emphasis on family, a mass migration out of the city occurs as almost everyone in Seoul heads back to his or her hometown during these dates. Anticipate for all modes of transportation to be extremely crowded. Also, many shops and restaurants close for Korean New Year, making the holiday not particularly tourist-friendly.
The shoulder seasons of spring and fall—March through May and October through November, respectively—are widely considered to be the best times to visit Seoul. Hotels and plane tickets are typically cheaper, and the weather is more temperate.
Low season consists of the winter months between December and February, with average daily temperatures in the high 20s to low 30s. For those who love snow, winter is a great time to visit Seoul, not only because of the lower prices, but also because there are a ton of winter activities for children and adults in and around the city. If you enjoy sledding, skiing, or ice fishing, Seoul in the winter makes for a very out-of-the-ordinary vacation spot.