<P> The Climate of India comprises a wide range of weather conditions across a vast geographic scale and varied topography, making generalisations difficult . Based on the Köppen system, India hosts six major climatic subtypes, ranging from arid desert in the west, alpine tundra and glaciers in the north, and humid tropical regions supporting rainforests in the southwest and the island territories . Many regions have starkly different microclimates . The country's meteorological department follows the international standard of four climatological seasons with some local adjustments: winter (December, January and February), summer (March, April and May), a monsoon rainy season (June to September), and a post-monsoon period (October to November). </P> <P> India's geography and geology are climatically pivotal: the Thar Desert in the northwest and the Himalayas in the north work in tandem to effect a culturally and economically important monsoonal regime . As Earth's highest and most massive mountain range, the Himalayas bar the influx of frigid katabatic winds from the icy Tibetan Plateau and northerly Central Asia . Most of North India is thus kept warm or is only mildly chilly or cold during winter; the same thermal dam keeps most regions in India hot in summer . </P>

When does the summer monsoon occur in india