Laos' climate is tropical in most plain areas, while it is subtropical in the far north and in the mountains. The country is affected by the monsoon: that of winter, which brings good weather and a freshness at night from November to February, and that of summer, which brings humid air and rains from May to mid-October. However, the monsoon is irregular: it does not always happen at the same time, and does not always have the same intensity. The period between March and May, before rains comming, is the hottest of the year, and it is quite dry, but some afternoon thunderstorms may occur; the summer months are humid. It is around 30/32°C, but the high humidity. April is the hottest month. It is around 35°C, sometimes 40/42°C in the center-south, and even 45°C in the north. In May the temperature begins to decrease in the south, while in the north, where the monsoon arrives later, it is still very hot, especially in the first part.
Rainfall in Laos is normally between 1,200 and 2,200 millimeters per year on the plains, and can exceed 3,000 mm on the slopes of the most exposed mountains. The rainiest months are generally August and September.