Argentina’s wine regions are widely dispersed, but are almost entirely confined to the western strip of the country bordering the foothills of the Andes, where the climate is continental, with the four seasons clearly defined. The vineyard area extends from the 23rd to the 42nd parallel in the south. Apart from the southern, largely fruit-growing areas of the Río Negro and Neuquén, the climate is semi-desert with annual rainfall rarely more than 250 mm/10 in.
Summer temperatures vary from 10 °C/50 °F at night to as much as 40 °C/104 °F during the day. Summers are hot in the regions of San Juan (except for the high elevation valleys of Pedernal and Calingasta), La Rioja, Catamarca, and the east of Mendoza (Santa Rosa, Rivadavia, San Martín, and Lavalle). In the Calchaquies Valley (Cafayate), upper Mendoza (Luján de Cuyo), Uco Valley (Tupungato, Tunuyán, and San Carlos), and Río Negro, summers are temperate to warm, making them Regions II and III in the Winkler system of climate classification. In winter, temperatures can drop below 0 °C/32 °F with occasional light snowfalls. Heavy winter snow in the high Andes is important as this ensures plentiful supplies of particularly pure water for the irrigation systems on which the vines depend.