Orographic lift occurs when an
air massIn meteorology, an air mass is a large volume of air defined by its temperature and water vapor content. Air masses cover many hundreds or thousands of square miles, and adopt the characteristics of the surface below them. They are classified according to latitude and their continental or...
is forced from a low
elevationThe elevation of a geographic location is its height above a fixed reference point, often the mean sea level. Elevation, or geometric height, is mainly used when referring to points on the Earth's surface, while altitude or geopotential height is used for points above the surface, such as an...
to a higher elevation as it moves over rising terrain. As the air mass gains
altitudeAltitude is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object...
it expands and cools adiabatically, which can raise the
relative humidityRelative humidity is a term used to describe the amount of water vapor that exists in a gaseous mixture of air and water vapor.- Definition :...
to 100% and create
cloudA cloud is a visible mass of droplets or frozen crystals suspended in the atmosphere above the surface of the Earth or another planetary body. A cloud is also a visible mass attracted by gravity, such as masses of material in space called interstellar clouds and nebulae...
s and, under the right conditions,
precipitationIn meteorology, precipitation is any product of the condensation of atmospheric water vapor that is deposited on the Earth's surface. The main forms of precipitation include rain, snow, ice pellets, and graupel...
.
Precipitation
Precipitation induced by orographic lift occurs in many places throughout the world. Examples include:
- The mountains near Baja California North - specifically La Bocana to Laguna Hanson.
- The windward slopes of Khasi and Jayantia Hills see over 11000 mm (see Mawsynram
Mawsynram is a village in the Khasi Hills of Meghalaya state in north-eastern India, 56 kilometers from Shillong. It is reportedly the wettest place on Earth, with an annual rainfall of 11,872 mm . According to the Guinness Book of World Records Mawsynram received an incredible 26,000mm in 1985...
) of rain during the Southwest Monsoon Season
- The Western Ghats
The Western Ghats also known as the Sahyadri Mountains, is a mountain range along the western side of India. It runs north to south along the western edge of the Deccan Plateau, and separates the plateau from a narrow coastal plain along the Arabian Sea...
that run along India's western coast.
- The eastern seaboard of Australia, which faces prevailing easterly winds.
- The Great Dividing Range
The Great Dividing Range, or the Eastern Highlands, is Australia's most substantial mountain range and the fourth longest in the world. The range stretches more than 3,500 km from Dauan Island off the northeastern tip of Queensland, running the entire length of the eastern coastline through...
of Eastern and South Eastern Australia which forces uplift of moist air originating from the oceans
- The mountains of New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses , and numerous smaller islands, most notably Stewart Island/Rakiura and the Chatham Islands. The indigenous Māori named New Zealand Aotearoa, commonly translated as The Land of the Long White Cloud...
, which faces a prevailing westerly flow off the Tasman SeaThe Tasman Sea is the large body of water between Australia and New Zealand, approximately 2000 kilometres across. It extends 2800 km from north to south. It is a south-western segment of the South Pacific Ocean. The sea was named after the Dutch explorer Abel Janszoon Tasman, the first...
.
- The mountainous western coastal regions of Tasmania
Tasmania is an Australian island and state. It is located south of the eastern side of the continent, from which it is separated by Bass Strait. The state includes the island of Tasmania – the 26th largest island in the world – and the surrounding islands. The state has a population of 500,000 ,...
which also face a prevailing westerly flow.
- The southern Andes
The Andes are the world's longest exposed mountain range. They lie as a continuous chain of highland along the western coast of South America...
, which faces a prevailing westerly flow off the Pacific OceanThe Pacific Ocean is the largest of the Earth's oceanic divisions. Its name is derived from the Latin name Tepre Pacificum, "peaceful sea", bestowed upon it by the Portuguese explorer Ferdinand Magellan. It extends from the Arctic in the north to Antarctica in the south, bounded by Asia and...
.
- The Northwestern United States
The Northwestern United States comprise the northwestern states up to the western Great Plains regions of the United States, and consistently include the states of Oregon and Washington, to which Idaho, Montana, Wyoming, Southeast Alaska, and parts of Northern California are sometimes added...
and CanadaCanada is a country occupying most of northern North America, extending from the Atlantic Ocean in the east to the Pacific Ocean in the west and northward into the Arctic Ocean...
(OregonOregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...
, WashingtonWashington is a state in the Pacific Northwest region of the United States. Washington was carved out of the western part of Washington Territory which had been ceded by Britain in 1846 by the Oregon Treaty as settlement of the Oregon Boundary Dispute. It was admitted to the Union as the...
and British ColumbiaBritish Columbia is the westernmost of Canada's provinces and is famed for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . In 1871, it became the sixth province of Canada.The capital of British Columbia is Victoria, the 15th largest metropolitan region in Canada...
) see prevailing westerly flow off the northern Pacific OceanThe Pacific Ocean is the largest of the Earth's oceanic divisions. Its name is derived from the Latin name Tepre Pacificum, "peaceful sea", bestowed upon it by the Portuguese explorer Ferdinand Magellan. It extends from the Arctic in the north to Antarctica in the south, bounded by Asia and...
. Places on the sea-facing side of coastal mountains see in excess of 140 inches (over 3.5 m) of precipitationIn meteorology, precipitation is any product of the condensation of atmospheric water vapor that is deposited on the Earth's surface. The main forms of precipitation include rain, snow, ice pellets, and graupel...
per year. These locales are on the side of the mountainA mountain is a large landform that stretches above the surrounding land in a limited area usually in the form of a peak. A mountain is generally steeper than a hill. The adjective montane is used to describe mountainous areas and things associated with them...
s which are in the path of stormA storm is any disturbed state of an astronomical body's atmosphere, especially affecting its surface, and strongly implying severe weather...
systems, and therefore receive the moisture which is effectively squeezed from the clouds.
- The ski country
Ski country is a term used to describe portions of the boundary between the Niagara Frontier and the Southern Tier of the western part of New York.-Weather:...
region of New YorkNew York is a state in the Mid-Atlantic and Northeastern regions of the United States and is the nation's third most populous. The state is bordered by New Jersey and Pennsylvania to the south, and Connecticut, Massachusetts and Vermont to the east...
and PennsylvaniaThe Commonwealth of Pennsylvania , often colloquially referred to as PA by natives and Northeasterners, is a state located in the Northeastern and Middle Atlantic regions of the United States...
, particularly with lake effect snowLake-effect snow is produced in the winter when cold winds move across long expanses of warmer lake water, providing energy and picking up water vapor which freezes and is deposited on the windward shores. The same effect over bodies of salt water is called ocean effect snow, sea effect snow, or...
s.
- Transylvania County, North Carolina
Transylvania County is a county located in the U.S. state of North Carolina. As of 2000, the population was 29,334. Its county seat is Brevard.- History :The county was formed in 1861 from parts of Henderson County and Jackson County...
, which gets the most rainfall of anywhere in the Eastern U.S. (90 inches).
- The Eastern seaboard of
Madagascar island, located in the Indian Ocean off the east coast of Africa, is the fourth largest island in the world. Its long isolation from neighbouring continents allowed the evolution of distinct communities of plants and animals. It is home to five percent of the world's plant and animal...
MadagascarMadagascar, or Republic of Madagascar , is an island nation in the Indian Ocean off the southeastern coast of Africa. The main island, also called Madagascar, is the fourth-largest island in the world, and is home to 5% of the world's plant and animal species, of which more than 80% are endemic to...
.
Rain shadowing
The highest precipitation amounts are found slightly upwind from the prevailing winds at the crests of mountain ranges, where they relieve and therefore the upward lifting is greatest. As the air descends the lee side of the mountain, it warms and dries, creating a rain shadow. On the lee side of the mountains, sometimes as little as 15 miles (25 km) away from high precipitation zones, annual
precipitationIn meteorology, precipitation is any product of the condensation of atmospheric water vapor that is deposited on the Earth's surface. The main forms of precipitation include rain, snow, ice pellets, and graupel...
can be as low as 8 inches (200 mm) per year.
Areas where this effect is observed include:
- The Himalayas
The Himalaya Range or Himalayas for short , meaning "abode of snow", is a mountain range in Asia, separating the Indian subcontinent from the Tibetan Plateau...
block moisture from the Tibetan PlateauThe Tibetan Plateau , also known as the Tibel-Qingai Plateau or Qinghai-Tibetan Plateau is a vast, elevated plateau in Central Asia covering most of the Tibet Autonomous Region and Qinghai Province in China and Ladakh in Kashmir, India...
- The Atacama Desert
The Atacama Desert is a virtually rainless plateau in South America, covering a strip of land on the Pacific coast of South America, west of the Andes mountains. The Atacama desert is, according to NASA, National Geographic and many other publications, the driest desert in the world...
in PeruPeru , officially the Republic of Peru , is a country in western South America. It is bordered on the north by Ecuador and Colombia, on the east by Brazil, on the southeast by Bolivia, on the south by Chile, and on the west by the Pacific Ocean.Peruvian territory was home to the Norte Chico...
and ChileChile, officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
- Switzerland
Switzerland , officially the Swiss Confederation , is a federal republic consisting of 26 states named cantons, with Bern as the seat of the federal authorities...
's Rhone valleyThe Rhone is one of the major rivers of Europe, originating in Switzerland and running from there through the south-eastern corner of France...
- Areas east of the Cascade Range
The Cascade Range is a major mountain range of western North America, extending from southern British Columbia through Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as the North Cascades, and the notable volcanoes known as the High Cascades...
in the Pacific Northwest (WashingtonWashington is a state in the Pacific Northwest region of the United States. Washington was carved out of the western part of Washington Territory which had been ceded by Britain in 1846 by the Oregon Treaty as settlement of the Oregon Boundary Dispute. It was admitted to the Union as the...
and OregonOregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...
)
- Areas east of the Olympic Mountains
The Olympic Mountains is a mountain range on the Olympic Peninsula of western Washington in the United States. The mountains are not especially high - Mount Olympus is the highest at - but the western slopes of the Olympics rise directly out of the Pacific Ocean and are the wettest place in the...
in Washington state
- The Great Basin
The Great Basin is a large, arid region of the western United States. Its boundaries vary depending on how it is defined, but it is most commonly defined as the contiguous endorheic basin roughly between the Wasatch Mountains and the Sierra Nevada mountains. Culturally, the Great Basin is home to...
of the United States, east of the Sierra Nevada
- Geography of the United States Pacific Mountain System
The Western Cordillera covers an extensive area of mountain ranges, basins, and plateaus in western North America...
- Pacific Cordillera
The Pacific Cordillera is a top-level physiographic region of Canada. The mountain ranges in this region were covered during the Pleistocene by the Cordilleran Ice Sheet...
- California
California is the most populous state in the United States, and the third largest by area. California is the second most populous sub-national entity in the Americas, behind only São Paulo, Brazil...
's Central Valley
- The Canadian Prairies
The Canadian Prairies is a region of Canada, specifically in Western Canada, which may correspond to several different definitions, natural or political. Notably, the Prairie provinces or simply the Prairies comprise the provinces of Alberta, Saskatchewan, and Manitoba, as they are much covered by...
- The Hawaii
Hawaii is the newest of the 50 U.S. states, and is the only state made up entirely of islands. It is located on an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of Australia. The state was admitted to the Union on August...
an island of KauaiKauai or Kauai is the oldest of the main Hawaiian Islands. With an area of , it is the fourth largest of the main islands in the Hawaiian archipelago and the 21st largest island in the United States...
- North East England is in the rain shadow of the Pennines, this combined with Britain's previaling wind from the South West. This explains the significant differences between the rainfall in the North West and North East.
Leeward winds
Downslope winds occur on the leeward side of mountain barriers when a stable air mass is carried over the mountain by strong winds that increase in strength with height. Moisture is removed and latent heat released as the air mass is orographically lifted. As the air mass descends, it is compression heated. The warm foehn wind, locally known as the
Chinook windChinook winds, often called chinooks, commonly refers to foehn winds in the interior West of North America, where the Canadian Prairies and Great Plains meet various mountain ranges, although the original usage is in reference to wet, warm coastal winds in the Pacific Northwest.Chinook is falsely...
,
BergwindBergwind is the South African name for a foehn wind, a hot dry wind blowing from the mountainous interior to the coast. It varies from mild to gusts up to 100km/h that cause structural damage...
or
Diablo windDiablo wind is a relatively recent term for a hot, dry offshore wind from the northeast that typically occurs in the San Francisco Bay Area of Northern California during the Spring and Fall. The same wind pattern also affects other parts of California's coastal ranges...
or "Nor-Wester" depending on the region, provide examples of this type of wind, and are driven in part by latent heat released by orographic-lifting-induced precipitation.
A similar class of winds, the
SiroccoSirocco, scirocco, jugo or, rarely, siroc is a Mediterranean wind that comes from the Sahara and reaches hurricane speeds in North Africa and Southern Europe. It is known in North Africa by the Arabic word qibli or ghibli Sirocco, scirocco, jugo or, rarely, siroc is a Mediterranean wind that comes...
, the
BoraBora may refer to:* Bora , a village in Punjab, India* Bora , a wind in Adriatic, Greece, Russia and Turkey* Bora language, a Witotoan language spoken in Peru, Brazil, and Colombia* Bora people, the ethnic group that speaks the Bora language...
and
Santa Ana windThe Santa Ana winds are strong, extremely dry offshore winds that characteristically sweep through in Southern California and northern Baja California in late fall into winter. They can range from hot to cold, depending on the prevailing temperatures in the source regions, the Great Basin and upper...
s, are examples where orographic lifting has limited effect since there is limited moisture to remove in the
SaharaThe Sahara , , "The Greatest Desert") is the world's largest hot desert. At over 9,000,000 square kilometres , it covers most of Northern Africa, making it almost as large as the United States or the continent of Europe. The desert stretches from the Red Sea, including parts of the Mediterranean...
n or other air masses; the Sirocco, Bora and Santa Ana are driven primarily by (adiabatic) compression heating.
Associated clouds
As air flows over mountain barriers, orographic lift can create a variety of cloud effects.
- Orographic fog is formed as the air rises up the slope and will often envelope the summit. When the air is humid, some of the moisture will fall on the windward slope and on the summit of the mountain.
- When there is a high wind, a banner cloud is formed downwind of the upper slopes of isolated, steep-sided mountains. This cloud is similar to the condensation observed off the tips of high-performance aircraft wings when they operate in humid conditions; it is created by the vortices
A vortex is a spinning, often turbulent,flow of fluid. Any spiral motion with closed streamlines is vortex flow. The motion of the fluid swirling rapidly around a center is called a vortex...
and local uplifting in the air caused by the orographic lifting as the wind passes the mountain. The most famous such cloud forms routinely in the lee of the MatterhornThe Matterhorn , Cervino or Cervin , is a mountain in the Pennine Alps. With its high summit, lying on the border between Switzerland and Italy, it is one of the highest peaks in the Alps and its north face is one of the Great north faces of the Alps...
..
- The leeward edge of an extensive mass of orographic clouds may be quite distinct. On the leeward side of the mountain, the air flows downwards. Because some of the moisture has condensed on the top of the mountain, the leeward air is drier. The remaining moisture quickly evaporates as the air descends. The distinct cut-off line which forms along and parallel to the ridge line is sometimes known as a foehn wall-(or föhn wall). This is because the edge appears stationary and it often appears to have an abrupt wall-like edge. A foehn wall is a common feature along the Front Range
The Front Range is a mountain range of the Rocky Mountains of North America that is located in the north-central portion of the U.S. State of Colorado...
of the ColoradoColorado is a U.S. state located in the Rocky Mountain region of the United States of America. It may also be considered to be part of the Western and Southwestern regions of the United States. Colorado entered statehood in 1876 and was nicknamed the “Centennial State”...
RockiesThe Rocky Mountains are a major mountain range in western North America. The Rocky Mountains stretch more than from the northernmost part of British Columbia, in Canada, to New Mexico, in the United States. The range's highest peak is Mount Elbert in Colorado at above sea level...
.
- A Rotor cloud is sometimes formed downwind and below the level of the ridge. It has the appearance of the ragged cumulus
Cumulus may refer to:*Cumulus cloud, a type of cloud*Cumulus Media, a radio broadcasting company*Cumulus , digital asset management software developed by Canto Software* Cumulus , GPL software synthesizer using grain synthesis...
cloud type but it is caused by a turbulent horizontal vortex, ie the air is very rough.
- Lenticular cloud
Lenticular clouds are stationary lens-shaped clouds that form at high altitudes, normally aligned perpendicular to the wind direction. Lenticular clouds can be separated into altocumulus standing lenticularis , stratocumulus standing lenticular , and cirrocumulus standing lenticular .- Formation...
s are stationary lens-shaped clouds that are formed downwind of mountains by lee wavesIn meteorology, lee waves are atmospheric standing waves. The most common form is mountain waves, which are atmospheric internal gravity waves...
if the air mass is close to the dew point. They are normally aligned at right-angles to the wind direction and are formed at altitudes up to .
- A cap cloud is a special form of the lenticular cloud with a base low enough that it forms around and covers the peak, capping it.
- A chinook arch cloud is an extensive wave cloud. It has this special name in North America where it is associated with the Chinook wind
Chinook winds, often called chinooks, commonly refers to foehn winds in the interior West of North America, where the Canadian Prairies and Great Plains meet various mountain ranges, although the original usage is in reference to wet, warm coastal winds in the Pacific Northwest.Chinook is falsely...
. It forms above the mountain range, usually at the beginning of a chinook wind as a result of orographic lifting over the range. It appears when seen from downwind to form an arch over the mountain range. A layer of clear air separates it from the mountain.