Laos enjoys a tropical climate with two distinct seasons - the rainy season from the beginning of May to the end of September and dry season from October through to April. The yearly average temperature is about 28 C, rising to a maximum of 38 C in April and May. In Vientiane minimum temperatures of 19 C are to be expected in January. In mountainous areas, however, temperatures drop to 14-15 C during the winter months, and in cold nights easily reach the freezing point.
The average precipitation is highest in southern Laos, where the Annamite mountains receive over 3000 mm annually. In Vientiane rainfall is about 1500-2000 mm, and in the northern provinces only 1000-1500 mm.