Climatic map of the Province of Tucumán, Argentina
Tucumán lies at the convergence of temperate climates and tropical climates further north, retaining characteristics of both in the lowlands. Furthermore, it is highly monsoonal, and depends also on elevation. As a rule of thumb, the far east is drier and hotter, whereas the Piedmont has many storms in the summer which moderate temperatures. The first foothills are very humid, provoking a dense jungle, and as altitude increases, a thick forest and then cool grasslands. The westernmost areas are once again a bit dryer because of a rain shadow.
The eastern parts have an average annual temperature of 18 to 20 °C. Summers are hot with mean temperatures averaging between 24 to 26 °C while in winter, the mean temperatures are between 10 to 12 °C. Easternmost parts of the province, which borders the Chaco region are home to the highest and lowest temperatures in the province where absolute maximum temperatures can exceed 40 °C while absolute minimum temperatures can reach close to ?7 °C owing to the accumulation of cold air that descends from the mountains. At higher altitudes, the climate is cooler with summer temperatures averaging 20 °C and winter temperatures averaging 10 °C. The annual temperature in the higher altitudes is 12 to 14 °C. at an altitude of 2,500 metres above sea level. Within the valleys located between the mountains, temperatures are cooler with a mean annual temperature of 13.1 °C (summers average 17.1 °C while winters average 9.0 °C) in the Tafi valley.
Precipitation in the lowlands ranges from 600 mm in the east, to close to 1,200 mm in the foothills, in a very monsoonal pattern with 4-5 completely dry winter months, and a peak of about 200 mm in the rainiest summer month.
The eastward-facing slopes concentrate not only the heaviest precipitation, with spots around 1,800 mm falling mostly in the 5 months of the summer monsoon, but also have a unique characteristic, which is that during part of the year, they are constantly immersed in a thick fog, providing humidity for the development of a thick jungle. The climate quickly becomes decidedly temperate with altitude, supporting different kinds of forest which even receive some snow every winter, finally reaching high-altitude grasslands with cool, windy weather year-round.
The abundant precipitation creates a wide area of abundant vegetation and justifies Tucumán's title of "Jardín de la República" (Garden of the Republic).