Mendoza has over 300 sunny days a year and a semi-arid climate that makes it pleasant to visit year-round, though the seasons shape the experience considerably.
March is the best single month for a first visit. The Fiesta de la Vendimia (National Grape Harvest Festival) falls in late February or early March, with the main events at the Frank Romero Day Amphitheatre on Cerro de la Gloria in Parque San Martín. The theatrical coronation of the Harvest Queen, the crowded harvest blessing at the Basilica of San Francisco, and the general carnival atmosphere around Plaza Independencia make this an exceptionally lively time. The weather is warm but no longer the peak summer heat.
April and May bring autumn colours to the vineyards, particularly in the Uco Valley where the vine leaves turn yellow and red against the Andean backdrop. Temperatures are mild and crowds thin after the harvest festival.
June to August is ski season. Mendoza city itself stays cool and pleasant; Las Leñas resort, about 450 kilometres to the south, draws serious skiers with reliable snowfall and long runs. Several smaller resorts closer to the city are also active. Aconcagua is off-limits to climbers in the deepest winter.
November to January is high summer — hot, sunny, and busy. The wine roads are crowded with tourists and bodega tastings fill up. Aconcagua's climbing season runs from November through March, so trekkers and mountaineers flood in from all over the world.
Best overall: late February through May for wine harvest, autumn colours, and comfortable temperatures. Winter for skiing. Avoid January if you dislike heat and crowds.