The climate in Laos is determined by the monsoons, and Laos falls within the monsoon belt of the tropics. The south-west monsoon, which blows between May and mid-October, brings the rains from moisture picked up in the Indian Ocean. The north-east monsoon, which lasts from November to February, brings cool, dry air from the interior of the continent resulting in mild and dry weather. As mountains cover most of Laos, there are significant climatic variations from region to region based on altitude. Precipitation is also highly variable with more falling on the western, windward slopes facing the south-west monsoon, than the eastern portion that lie in the lee during the rainy season.