Orographic lift occurs when an air mass is forced from a low elevation to a higher elevation as it moves over rising terrain. Orography is the study of the topographic relief of mountains. As the air mass gains altitude it quickly cools down adiabatically, which can raise the relative humidity to 100% and create clouds and, under the right conditions, precipitation.
Orographic lifting can have a number of effects, including precipitation, rain shadowing, leeward winds, and associated clouds.
Lake-effect snow is produced during cooler atmospheric conditions when a cold air mass moves across long expanses of warmer lake water. The lower layer of air, heated by the lake water, picks up water vapor from the lake and rises through colder air. The vapor then freezes and is deposited on the leeward (downwind) shores.
The same effect also occurs over bodies of saline water, when it is termed ocean-effect or bay-effect snow. The effect is enhanced when the moving air mass is uplifted by the orographic influence of higher elevations on the downwind shores. This uplifting can produce narrow but very intense bands of precipitation, which deposit at a rate of many inches of snow each hour, often resulting in a large amount of total snowfall.
A rain shadow is an area of significantly reduced rainfall behind a mountainous region, on the side facing away from prevailing winds, known as its leeward side.
Evaporated moisture from bodies of water (such as oceans and large lakes) is carried by the prevailing onshore breezes towards the drier and hotter inland areas. When encountering elevated landforms, the moist air is driven upslope towards the peak, where it expands, cools, and its moisture condenses and starts to precipitate. If the landforms are tall and wide enough, most of the humidity will be lost to precipitation over the windward side (also known as the rainward side) before ever making it past the top. As the air descends the leeward side of the landforms, it is compressed and heated, producing Foehn winds that absorb moisture downslope and cast a broad "shadow" of dry climate region behind the mountain crests. This climate typically takes the form of shrub–steppe, xeric shrublands, or deserts.
A Foehn, or Föhn (German pronunciation: [føːn], UK: /fɜːn/, US: /feɪn/ fayn, US also /fʌn, fɜːrn/ fu(r)n), is a type of dry, relatively warm downslope wind in the lee of a mountain range. It is a rain shadow wind that results from the subsequent adiabatic warming of air that has dropped most of its moisture on windward slopes (see orographic lift). As a consequence of the different adiabatic lapse rates of moist and dry air, the air on the leeward slopes becomes warmer than equivalent elevations on the windward slopes.
Foehn winds can raise temperatures by as much as 14 °C (25 °F) in just a matter of hours. Switzerland, southern Germany, and Austria have a warmer climate due to the Foehn, as moist winds off the Mediterranean Sea blow over the Alps.
Trade wind cumulus (or trade cumulus) clouds are formed by cooling and moisture absorption of the dry trade winds over the relatively cold sea surface in the eastern parts of the oceans. These are clouds, typically Cumulus humilis or Cumulus mediocris, which are considered as fair weather clouds.
Characteristic for trade wind clouds is the uniform height of the upper cloud limit, which typically lies between 1000 and 1500 meters and thus indicates the altitude of the trade wind inversion. Due to orographic lift at mountains, the clouds can also rise higher, but the trade wind inversion also limits a further rise here, so that even in this case a light drizzle can occur at best. At night, the trade wind clouds usually dissipate again, especially over land.
The climate of India includes a wide range of weather conditions, influenced by its vast geographic scale and varied topography. Based on the Köppen system, India encompasses a diverse array of climatic subtypes. These range from arid and semi-arid regions in the west to highland, sub-arctic, tundra, and ice cap climates in the northern Himalayan regions, varying with elevation.
The Indo-Gangetic Plains in the north experience a humid subtropical climate which become more temperate at higher altitudes, like the Sivalik Hills, or continental in some areas like Gulmarg. In contrast, much of the south and the east exhibit tropical climate conditions, which support lush rainforests in parts of these territories. Many regions have starkly different microclimates, making it one of the most climatically diverse countries in the world. The country's meteorological department follows four seasons with some local adjustments: winter (December to February), summer (March to May), monsoon or south-west monsoon (June to September) and post-monsoon or north-east monsoon (October to November). Some parts of the country with subtropical, temperate or continental climates also experience spring and autumn.