Weather will likely play an important role when you plan your trip to Phonsavan, but bear in mind that cheaper options are usually available when the weather isn't as good. The hottest months are usually April and March, with an average temperature of 22°C, while the coldest months are January and December, with an average of 17°C. The rainiest months in Phonsavan are August, July, June and May, with each month seeing an average of 268 mm of rainfall.