Situated entirely east of the Pacific coastal desert, Bolivia divides neatly into lowland and highland regimes. The lowlands include rainforest across the northeast and the Chaco grasslands across the southeast. Both regions are hot and humid – it often climbs above 40°C/104°F across the Chaco from September to December – and both get plenty of rain from November to April, with the amounts heavier in the north but the Chaco plains often turning to swampland in the wet season.
Many adventurers come to Bolivia's altiplano, a vast plateau with an average elevation of 3800ft/12,500ft. Since it is lower in both altitude and latitude than the even larger Tibetan plateau, the altiplano is cut off from any weather that the mid-latitude jet stream might deliver (though the sub-tropical jet may bring fierce winds at times). The altiplano's climate is driven mainly by its extreme aridity and the intense tropical sun. Temperatures typically vary by at least 20°C/36°F between day and night; Charana once recorded a phenomenal daily range of 42°C/75°F. These day-to-night contrasts are especially great in autumn (March–May). Nights can dip far below freezing and afternoons can climb above 10°C/50°F, even in mid-winter. La Paz sits just below the altiplano's north edge, helping it to remain milder on the coldest nights. Winter days on the altiplano tend to be crystal-clear, with only a handful of light snows each year. The mild summer afternoons often bring a quick, intense round of thunder, sometimes dropping sleet or snow that quickly disappears.