June-July are dry and sunny but bitterly cold in the highlands. This is a good time to travel – as long as you have packed well. While the days are still warm, nighttime temperatures can drop to -20°C, and some tours have pre-dawn starts. Brrr!
August is also chilly, as well as being the busiest month. This means early booking is essential, and prices are also likely to be higher.
The Amazon is pleasantly fresh in the dry winter months, as the humidity drops along with the temperatures. While it is still warm – frequently reaching 30°C – cold spells called surazos blow in periodically from the south, meaning the temperature can drop to 12°C overnight, and remain cool for a few days.
November to March is the rainy season. This disrupts both road and air travel, particularly from January onwards, as roads can flood, landslides are common and fog and cloud can make driving or hiking in the mountains dangerous. January to March is not the best time to visit Bolivia if you plan to do outdoor activities such as hiking or cycling. However, the dusty landscape does make a wonderful transition to green, and wildflowers bloom on the mountain slopes.
The lowlands bear the brunt of the flooding (though river travel does become easier, for intrepid adventurers), and biting insects increase.
Flights are also frequently disrupted by poor weather (and strikes, and protests…) so if you have to be in a particular place at a particular time (ie. returning to La Paz for an international flight home) it is strongly advised to arrive the day before and call ahead to confirm departure.
You may have seen magical, mirror-like photographs of the flooded Salt Flats – a beautiful optical illusion during the rainy season. However, while you can still visit the edge of the Salar when it is flooded, you will not be able to cross it or visit the island in the middle.
The majority of festivals fall from February to April, such as Carnival and Easter (Holy Week). These could form a key part or your trip, or be an inconvenient disruption to travel if roads or attractions are closed. So check with your operator before you go!