The Copiapo river (27S) marks the southern border of an extreme arid desert that dominates most of the region west of the Andes from the Ecuador/Peru border. The region is isolated by the Andes of any moisture coming from the Amazon, that only sometimes reaches the Chilean and Bolivian Aliplano during the summer months (Jan-March),
these winds are cncecuence of the Bolivian high that establishes itself aver BOlivia strongly during the summer months. South of Copiapo and to about 31S the region is still dry, but occasional polar front reach the region during the winter so that annual rainfall gradually reaches about 500 mm per year. The temperature variations in the north of Chile are very small, with an annual range of less than 7C. Stratus clouds are very common during winter at the coast and about half of the time during summer.
 
 

PRECIPITATION	TEMPERATURE

WET-DAY FREQUENCY Number of days/mo with Precipitation	GROUND-FROST FREQUENCY Number of days/mo with Min. Temp. < 0 deg. C