year. In the warmest regions (such as Catamarca, La Rioja, San Juan and the eastern outreaches of Mendoza), summer temperatures during the growing season can be very hot during the day with temperatures upwards of . Nighttime temperatures can drop to creating a wide diurnal temperature variation. Some regions have more temperate climates such as the Cafayate region of Salta, Río Negro and the western reaches of Mendoza which includes the Luján de Cuyo and Tupungato departments. Wintertime temperatures can drop below but frost is a rare occurrence for most vineyards, except those planted at extremely high altitudes with poor air circulation. Most rainfall occurs during the summer months and in late summer sometimes fall as hail (known as La Piedra), posing potential damage to the vines. These warmer regions can see an average of 320 days of sunshine a year. The northwestern wine regions are particularly prone to the effects of the hurricane force winds known as the Zonda which blows from the Andes during the flowering period of early summer. This fierce wind of hot, dry air can disrupt the flowering process and severely reduce potential yields. Most of the growing season is dry with the lack of humidity limiting the risk and hazard from various grape diseases and fungal rot. Many vineyards operate without the need for any chemical spraying, a condition conducive to organic viticulture. The periodic occurrence of the El Niño phenomenon can have a sharp influence on climate condition during a growing season-such as the case during the 1998 vintage when prolong heavy rains brought by El Niño led to widespread rot and fungal disease. The Andes Mountains are the dominant geographical feature of Argentine wine regions, with the snow-capped mountains often serving as a backdrop view to the vineyards. As the winter snows start to melt in the spring, an intricate irrigation system of dams, canals and channels brings vital water supplies down to the wine regions to sustain viticulture in the dry, arid climates. Most of the wine regions are located within the foothills of the Andes and recent trends have seen a push to plant vineyards on higher elevations closer to the mountains. The climate in some of this regions can be more continental and less prone to extremes in temperatures. Soils throughout the country are mostly alluvial and sandy with some areas having substrates of clay, gravel and limestone. In