South Korea has four distinct seasons, and the best times to visit are in the spring and fall, since summers are hot and wet and winters are dry and very cold -- though the mountainous terrain makes for great skiing. More detailed weather information is given below, but a far bigger factor in your planning should be avoiding major Korean holidays. Domestic tourists take to the roads in the tens of thousands, crowding all forms of transportation, filling hotels, and making it difficult to visit popular attractions. By contrast, Seoul empties out and traffic is almost nonexistent.
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Seol (Lunar New Year) -- Although January 1 is also celebrated in South Korea, Seol (also known as Seollal) is a bigger holiday. It can be difficult for tourists to figure out when the Lunar New Year will fall, as Westerners rely on a solar calendar. The solar calendar equivalents of the Lunar New Year for the next few years are February 3, 2011; January 23, 2012; February 10, 2013. Most Koreans get 3 days off during the holiday and use that time to travel to their hometowns. Others take the opportunity to go on ski holidays or travel abroad. Bus and train tickets go on sale 3 months before the holiday and people line up for hours in order to get their passage out of town. Driving is a bad option, since the normal 5- to 6-hour drive from Seoul to Busan, for example, can take up to 14 hours due to ridiculous traffic.
Children's Day -- Though not necessarily in prime travel season, May 5 is the day South Koreans celebrate their little ones. Parents dress up their kids and take them to amusement parks, zoos, theaters -- pretty much anywhere children love to go. If you want to avoid big crowds, stay away from kiddie hot spots on this day.
Summer Holidays -- It's not as insanely busy as the Lunar New Year or Chuseok , but when the kids go on summer break, many families head out of Seoul to vacation on the beaches and in the mountains. Korean children have only about 6 weeks of summer vacation, usually from mid-July to late August, but university students keep trains and buses busy throughout the season. Be sure to book rooms in popular destinations (such as Busan's beaches, which get super-crowded June-Aug) well in advance.
Chuseok (Harvest Moon Festival) -- Another traditional holiday as important as Lunar New Year, Chuseok (sometimes spelled Chusok) is celebrated on the 15th day of the eighth lunar month, usually sometime in mid- to late September. Solar equivalents for the next few years are September 22, 2010; September 12, 2011; September 30, 2012; and September 19, 2013. The days before and after are considered legal holidays in South Korea. Once again, Korean families mobilize to visit their hometowns and pay respect to their ancestors. Tickets for travel usually sell out 3 months in advance and roads and hotels are again packed.
South Korea's climate can be described as temperate, with four distinct seasons. The weather is heavily influenced by the oceans that surround the Korean Peninsula and by its proximity to the rest of Asia to the north. Winters and summers are long and punctuated by short but enjoyable springs and autumns.
Winter begins in November as cold air moves south from Siberia and Manchuria. By December and January, average temperatures drop below 32°F (0°C) over the whole country, with the notable exception of Jeju-do and some coastal areas. In Seoul, winter temperatures usually drop to 18°F (-8°C) and have been known to fall to -11°F (-24°C).
Spring starts by the end of March, when warm air begins to move north off the Pacific Ocean. Temperatures usually average 51°F (11°C), and rainfall is unpredictable. By the end of May, summer brings a period of warmth and humidity with heavy rainfall that starts in July and lasts until the end of September. Summer temperatures average 77°F (25°C), but often approach 86°F (30°C) in July and August. It's not the heat; it's the humidity. South Korea gets about 125cm (49 in.) of rain annually, 60% of which falls during the summer months. In general, the southern and western regions see more rain, with Jeju-do having the highest average rainfall per year. The summer is also typhoon season in South Korea. Although most typhoons lose their strength by the time they make it to the peninsula, some cause flooding, structural damage, and, in extreme cases, even death.
By late September, the cool, dry winds from Siberia change the weather again. Temperatures fall to about 59°F (15°C) and skies generally remain clear and crisp, with very little rainfall. Koreans consider autumn the best season, marked by the most important national holiday, Chuseok, when people visit their ancestral homes and give thanks for the harvest. Trees throughout the country exchange their summer greens for autumn colors.
South Koreans celebrate both holidays from the traditional lunar calendar (dates vary from year to year) and holidays adopted from the Western calendar. National public holidays are New Year's Day (celebrated Jan 1 and 2), Lunar New Year's Day (usually in Jan or Feb, and the 2 days following it), Independence Movement Day (Mar 1), Arbor Day (Apr 5), Children's Day (May 5), Buddha's Birthday/Feast of the Lanterns (the eighth day of the fourth month, usually in Apr or May), Memorial Day (June 5), Constitution Day (July 17), Liberation Day (Aug 15), Foundation Day (Oct 3), Harvest Moon Festival (14th-16th days of the eighth month), and Christmas Day (Dec 25).
Banks, schools, post offices, and government departments are all closed on the above dates, as are many museums and attractions. Although not a national holiday, Labor Day is observed on May 1, and banks and many businesses close.
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.