This is the world's most linear country: Chile spans 38° of latitude but less than 2° of longitude at its narrowest point. All along that length, the Andes and the Pacific face off. This means the gradual transition from sub-tropic to sub-polar along Chile's length is rivalled by the changes that occur in a short trip from coastline to mountaintop.
The coastal dryness that begins in Ecuador and extends through Peru reaches its arid apex in the Atacama Desert of northern Chile. The coastlines and nearby hills of Antofagasta and Tarapaca don't even get the drizzle that eases conditions further north and south: this region can go years without any moisture at all. (Arica averages less than 1mm/0.04in a year.) In winter, the low coastal overcast often breaks, leaving a bright, but cool, afternoon. Most summer days are crystal clear and just warm enough to feel slightly humid. It can get considerably hotter just inland from the coast, however. Like the nearby Bolivian altiplano, the Andes highlands of northern Chile experience huge daily temperature ranges year round and raw, chilly summer storms that seem to produce more thunder and lightning than precipitation. It's so dry that, despite altitudes of up to 6700m/22,000ft, there are no glaciers here.
Central Chile is a transition zone. The prevalence of winter rain and fog on the coast picks up south of La Serena (about 30°S). At Concepcion (about 37°S), you can expect a summer shower about once a week. At Valdivia (40°S) it's closer to once every three days in summer – and almost every day in mid-winter, when a month can easily deliver 300mm (10in). Just inland, the high valley that cradles Santiago eases into the agricultural Central Valley to the south. This belt is far more continental than the coast: daily temperature swings are large (though less so as you move south). Summer afternoons are warm with little rain or thunder; winters are chilly with bouts of mostly light rain, although floods can occur, and in spring, a round of downslope wind can push temperatures pleasantly upwards and quickly strip the western Andes slopes of their snow.
The islands and mountains of far southern Chile are perpetually raked by the Roaring Forties and Screaming Fifties, the incessant west winds that strike in these latitudes after crossing the Pacific. Patagonia's reputation for wind is well earned: across the Magellan Islands, the winds reach gale force on most afternoons, and hurricane speeds aren't uncommon at elevation. Summer is actually the windiest season here. Even at sea level, temperatures are low enough in summer (average highs are well below 20°C/68°F) so that it feels almost as raw as winter (when the temperature hovers close to freezing at sea level, and colder still at elevation). As for rain and snow, location is everything. West-facing slopes here are among the wettest on Earth for such high latitudes; some of the Magellans squeeze out more than 6000mm/236in of liquid in a typical year. The amounts drop off slightly south of 52°S. Points east of the higher terrain, such as Punta Arenas, tend to be semi-arid, with lots of cloud and rain or snow that's usually light.