The Andes affect the climate by influencing precipitation. In northern Colombia three ranges spread out to catch and hold the moisture of the northeastern trade winds, making this a region of heavy rainfall. On the Pacific side, from the Isthmus of Panama to the equator, the Colombian Andes catch the southwesterly winds, and rains fall almost daily. From the Gulf of Guayaquil through northern Chile, the west coast is extremely dry. This stretch lies in the trade wind belt.
Winds tend to come from the east and southeast, and they drop their moisture on the eastern slopes.
In summer they have moisture enough to give rain also on the western slopes. In northern Chile cool trade winds from the Pacific become warmed as they reach the hot coast and hold their moisture as fog. The great desert of Chile is one of the driest places in the world. Farther south the winds come from the west all through the year, and the Chilean slopes of the Andes catch their moisture as drenching rain or heavy snow. The eastern slopes in Argentina are relatively dry.