Weather details are given below, but a far bigger factor in your calculations should be the movement of domestic tourists who, during the longer public holidays, take to the road in the tens or even hundreds of millions, crowding all forms of transportation, booking out hotels, and turning even the quietest tourist sights into litter-strewn bedlam.
Peak Travel Seasons
Chinese New Year (Spring Festival): Like many Chinese festivals, this one operates on the lunar calendar. Solar equivalents for the next few years are February 6, 2008; February 25, 2009; and February 13, 2010. The effects of this holiday are felt from 2 weeks before the date until 2 weeks after, when anyone who's away from home attempts to get back, including an estimated 150 million migrant workers. Although tens of thousands of extra bus and train services are added, tickets for land transport are very difficult to get, and can command high prices on the black market (official prices also rise on some routes, and on ferries between Hong Kong and the mainland). Air tickets are usually obtainable and may even still be discounted. In the few days immediately around the new year, traffic on long-distance rail and bus services may be light, but local services may dry up altogether. Most tourist sights stay open, although some shut on the holiday itself or have limited holiday hours.
Labor Day and National Day: In a policy known as "holiday economics," the May 1 and October 1 holidays have now been expanded to 7 days each (including one weekend). These two holidays now mark the beginning and end of the domestic travel season, and mark the twin peaks of leisure travel, with the remainder of May, early June, and September also busy. Most Chinese avoid traveling in the summer except to cooler high ground or an offshore island, usually on a weekend. The exact dates of each holiday are not given out until around 2 weeks before each takes place, but it's best, if you're traveling independently, to arrive at a larger destination before the holiday starts, and move on in the middle or after the end. The disposable income to fund travel is more often found in larger cities, so these tend to become quieter, easier to get around, and less polluted. Noted tourist destinations around the country will be extremely busy, however. In Hong Kong and Macau, these are only 1- or 2-day holidays introduced in 1997 and 1999 respectively.
University Holidays Exact term dates are rarely announced far in advance, but train tickets can be difficult to obtain as the student populace moves between home and college. Terms run for 18 weeks with 2 weeks of exams, from the beginning of September to just before Spring Festival, and from just after the Spring Festival to the end of June.
Local Difficulties China's main international trade fair occupies the last 2 weeks of April and October, and drives up hotel prices in Guangzhou where it's held, and as far away as Hong Kong. In the summer, pleasant temperatures in the Northeast (slightly cooler than the rest of China) draw students on summer vacation (which makes train tickets hard to acquire), as well as large Chinese tour groups; it may not be the best time for your visit. The northeast's Dalian is also overbooked during the International Fashion Festival in September. Across China, midweek travel is always better than weekend travel, particularly true at destinations easily tackled in a weekend, such as Wutai Shan and Pingyao. Government-imposed travel restrictions in Tibet tend to increase around the Monlam Festival (sometime mid-Jan to mid-Feb), Saka Dawa Festival (mid-May to mid-June), and around the present Dalai Lama's birthday (July 6). The border crossing between Hong Kong and the mainland at Lo Wu can take a couple of hours at holiday periods.
China is the third-biggest country in the world, with the second-lowest inland depression (Turpan) and some of its highest peaks (Everest and K2 are both partly in China). Its far northeast shares the same weather patterns as Siberia, and its far southwest the same subtropical climate as northern Thailand.
In the north, early spring and late autumn are the best times to travel, both offering warm, dry days and cool, dry evenings. During March and April winds blow away the pollution but sometimes bring sand from the Gobi and topsoil from high ground to the northeast of Beijing, increasingly desiccated by the mismanagement of water resources. The sky can at times turn a vivid yellow.
In the south, November to February brings a welcome drop both in temperature and in all-pervasive humidity, although in Hong Kong all public interiors and many private houses are air-conditioned year-round.
Central China has some of the country's most searing summer temperatures and bitterest winters, but it also escapes the worst of the humidity. Tibet has springlike days in the summer but far milder winters than most people expect, at least in Lhasa, made endurable by the dryness of the climate. The northwest has perhaps the greatest range of temperatures, with severe summers and winters alike, but it is also largely dry.
Mainland China -- A few years ago the Chinese were finally granted a 2-day weekend. Offices close, but stores, restaurants, post offices, transportation, sights and, in some areas, banks, all operate the same services 7 days a week. Most sights, shops, and restaurants are open on public holidays, but offices and anything government-related take as much time off as they can. Although China switched to the Gregorian calendar in 1911, some public holidays (and many festivals -- see below) are based on a lunar cycle, their solar dates varying from year to year. Holidays are New Year's Day (Jan 1), Spring Festival (Chinese New Year and the 2 days following it), Labor Day (May 1 plus up to 4 more weekdays and a weekend), National Day (Oct 1 plus extra days, as with Labor Day, above).
Hong Kong -- Saturday is officially a working day in Hong Kong, although many offices take the day off or only open for reduced hours. Weekend ferry sailings and other transport may vary, particularly on Sunday, when many shops are closed and opening hours for attractions may also vary. Hong Kong gets many British holidays, traditional Chinese holidays, plus modern political ones added after 1997, but in shorter forms. Banks, schools, offices, and government departments are all closed on these dates, as are many museums: New Year's Day (Jan 1), Lunar New Year's Day (for the mainland Spring Festival, but in Hong Kong the day itself plus 2 more, and an extra Fri or Mon if 1 day falls on a Sun); Ching Ming Festival (Apr 5), Good Friday (usually early Apr, plus the following Sat and Easter Monday), Labor Day (May 1), Buddha's Birthday (1 day in May), Tuen Ng (Dragon Boat Festival, 1 day in June), Hong Kong SAR Establishment Day (July 1), Mid-Autumn Festival (1 day in Sept, usually moved to the nearest Fri or Mon to make a long weekend), National Day (Oct 1), Chung Yeung Festival (1 day in Oct), Christmas Day and Boxing Day (Dec 25, and the next weekday if the 26th is a Sat or Sun).
Macau -- Macau has the same holidays as Hong Kong except for SAR Establishment Day, and with similar consequences, but with the following variations: National Day is 2 days (Oct 1-2), All Souls' Day (Nov 2), Feast of the Immaculate Conception (Dec 8), Macau SAR Establishment Day (Dec 20), Winter Solstice (Dec 22), and Christmas Eve and Christmas Day (Dec 24-25).
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