As one would expect in a country that extends so far from north to south, Chile has many different climatic zones. All are cooled by the Humboldt current which originates in sub-Antarctic waters off the Pacific coast. The Humboldt current together with the prevailing southwesterly winds creates a temperate climate in most of northern and central Chile, even in areas that lie in tropical latitudes. Chile has many mountain rain shadows and micro climates.
Since Chile lies deep in the southern hemisphere, the seasons fall at opposite times of year from the northern hemisphere. Thus, the summer months are December, January, and February, while June, July and August are the winter months. When it is spring in North America or Europe, it is autumn in Chile Patagonia and vice versa. January, February, and March are the peak travel months. Needless to say, it is essential to take the inversion of seasons into account when planning your Chile fly fishing trip. December through April is the extent of the fly fishing season for trout in Chile's Patagonia.
Santiago boasts an ideal climate, which explains why 80% of Chile's population lives there. In Santiago, the seasons are well defined with hot summers (maximum 28°C to 32°C (82°F to 90°F); and short, temperate winters, with temperatures occasionally dipping to 0°C (32°F); fall and spring are cool, with pleasant breezes. Rainfall is generally restricted to the winter months. Humidity is low, thus reducing the disagreeable effects of heat and cold.
Chile's far south has a cool, damp climate. Severe cold is rare except at higher elevations. The moderating effect of the ocean prevents extreme heat waves in the summer and keeps temperatures from falling very low in the winter. Thus there is little difference in temperature from one season to the next in many regions. Average annual temperatures are 6° C (43° F) at Punta Arenas in the far south, 11° C (52° F) at Puerto Montt further north, 14° C (57° F) at Santiago, 16° C (61° F) at Antofagasta and 18° C (64° F) at Arica in Chile's far north.
Rainfall, on the other hand, is more variable. North of 27° south latitude, there is virtually no rainfall at all. Moisture comes mostly in the form of heavy mists. In north-central Chile, rainfall is heaviest in the winter months. As a general rule, precipitation increases as you head south (excepting some micro climates* rain shadow areas created by mountain ranges), culminating in south-central Chile, where it rains throughout the year and sometimes heavily. The area around Cape Horn can often be stormy. Rainfall tends to be lighter in some other parts of the far south such as Punta Arenas, which falls in the rain shadow of the drier eastern slopes of the Andes.
Chile can be divided into three major climatic areas — very arid in the far north, cool and damp in the south, and what can be characterized as a temperate Mediterranean climate in central Chile, with pronounced seasonal differences: heavier rainfall in the cooler months from May to August, and sunshine the rest of the year. It does occasionally snow in Santiago and other parts of central Chile, but the snow usually melts quickly except in the higher mountains. In the north, the interior of the Atacama Desert has some of the world's lowest amounts of precipitation and highest levels of solar radiation.