Laos is the only landlocked country in Southeast Asia, and it lies mostly between latitudes 14° and 23°N (a small area is south of 14°), and longitudes 100° and 108°E. Its thickly forested landscape consists mostly of rugged mountains, the highest of which is Phou Bia at 2,818 meters (9,245 ft), with some plains and plateaus. The Mekong River forms a large part of the western boundary with Thailand, whereas the mountains of the Annamite Range form most of the eastern border with Vietnam and the Luang Prabang Range the northwestern border with the Thai highlands. There are two plateau, the Xiangkhoang in the north and the Bolaven Plateau at the southern end. The climate is tropical and influenced by the monsoon pattern.
There is a distinct rainy season from May to November, followed by a dry season from December to April. Local tradition holds that there are three seasons (rainy, cold and hot) as the latter two months of the climatologically defined dry season are noticeably hotter than the earlier four months. The capital and largest city of Laos is Vientiane and other major cities include Luang Prabang, Savannakhet, and Pakse.
In 1993 the Laos government set aside 21 percent of the nation's land area for habitat conservation preservation. The country is one of four in the opium poppy growing region known as the "Golden Triangle". According to the October 2007 UNODC fact book Opium Poppy Cultivation in South East Asia, the poppy cultivation area was 15 square kilometers (5.8 sq mi), down from 18 square kilometers (6.9 sq mi) in 2006.
Laos has three distinct seasons. The hot season is from Mar-May, when temperatures can soar as high as 40°C. The slightly cooler wet season is from May-Oct, when temperatures are around 30°C, tropical downpours are frequent (especially Jul-Aug), and some years the Mekong floods.
The dry season from Nov-Mar, which has low rainfall and temperatures as low as 15°C (or even to zero in the mountains at night), is "high season" (when the most tourists are in the country). However, towards the end of the dry season, the northern parts of Laos — basically everything north of Luang Prabang — can become very hazy due to farmers burning fields and fires in the forests.
Source : https://en.wikipedia.org/wiki/Laos