The best time to travel is during the relatively cool and dry winter months from October/November to March when the temperature averages around 20°C. Not only is the weather more pleasant at this time of year but the roads are also in better shape. However, temperatures in upland areas, like the Plain of Jars and the Bolaven Plateau, can be surprisingly cold during these months, dropping as low as 8°C at night. In mountainous Xieng Khoung Province, temperatures can drop to freezing point in December and January.
The second half of the dry season, from April through to the first rains in May or June, sees temperatures soar to up to 40°C in many lowland areas. In the north, it can be every hazy as smoke from burning off the secondary forest hangs in the air. This can cause itchiness of the eyes. What’s more, it means that views are restricted and sometimes flights are cancelled.
During the rainy season, from June through to September/October, the tropical lowlands receive an annual average rainfall of 1250 mm a year. Temperatures during these months are 30-40°C. Average rainfall in Vientiane is 1700 mm, although in Northern Laos and the highlands it is much wetter, with more than 3000 mm each year. From June or July, as the wet season wears on, unsurfaced roads begin to deteriorate and overland transport in some areas becomes difficult.