There are 3 main regions in Bolivia: the Altiplano (highlands) in the west, the central highlands in the south-central region just beyond the Andes, and the tropical lowlands in the east, including the Amazon Basin.
The dry (winter) season in the Altiplano is from May to October and the wet (summer) season is from November to March. The difference is that the dry season has warm daytime temperatures (freezing at night) and occasional rainfall, while the summer has more humidity and more frequent rain showers. La Paz is located near the western border of Bolivia in the altiplano, at an elevation of 3300 to 4000 meters (10,600 to over 13,000 feet). Altitude sickness is common for foreigners upon arrival in La Paz (see Staying Healthy below).
Even in the warmer, more arid areas such as Uyuni and Potosi, the nights can dip below freezing at night and can even get cold during the day. Cold winds coming up from Patagonia can streak through the desert. So, pack a sweater or fleece.
The central highlands have comfortable temperatures and little rainfall year-round.
The Amazon Basin in the east is hot, humid, and rainy. Average temperatures are 30-32° C (85-90° F) during the day, and 20° C (68° F) at night.
