
Berg wind (from
Afrikaans
Afrikaans is a West Germanic languages, West Germanic language spoken in South Africa, Namibia and to a lesser extent Botswana, Zambia, Zimbabwe and also Argentina where there is a group in Sarmiento, Chubut, Sarmiento that speaks the Pat ...
''berg'' "mountain" + ''wind'' "wind", i.e. a mountain wind) is the
South African name for a
katabatic wind
A katabatic wind (named ) is a downslope wind caused by the flow of an elevated, high-density air mass into a lower-density air mass below under the force of gravity. The spelling catabatic is also used. Since air density is strongly dependent o ...
: a hot dry wind blowing down the
Great Escarpment from the high central plateau to the coast.
Overview
When the air that has been heated on the extensive central plateau flows down the escarpment to the coast, it undergoes further warming by
adiabatic process
An adiabatic process (''adiabatic'' ) is a type of thermodynamic process that occurs without transferring heat between the thermodynamic system and its Environment (systems), environment. Unlike an isothermal process, an adiabatic process transf ...
es. This accounts for the hot and dry properties of these offshore winds, wherever they occur along South Africa's coastline.
Although berg winds are often called
Föhn wind
A Foehn, or Föhn (, , , ), is a type of dry, relatively warm katabatic wind, downslope wind in the leeward, 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 ...
s, this is probably a misnomer, as Föhn winds are
rain shadow
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 body of water, bodies of water (such as oceans and larg ...
winds that result from air moving over a mountain range, resulting in precipitation on the windward side. This releases
latent heat
Latent heat (also known as latent energy or heat of transformation) is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process—usually a first-order phase transition, like melting or condensation. ...
into the atmosphere, which is then warmed still further as the air descends on the leeward side (e.g. the
Chinook or the original Föhn).
Berg winds do not originate in precipitation, but in the
mostly dry, often arid central plateau of
Southern Africa
Southern Africa is the southernmost region of Africa. No definition is agreed upon, but some groupings include the United Nations geoscheme for Africa, United Nations geoscheme, the intergovernmental Southern African Development Community, and ...
. On the other hand,
katabatic winds are technically drainage winds, which carry high density, usually cold, air from a high elevation down a slope under the force of gravity.
These are thus "fall winds", which occur most typically down the coastal ice slopes of
Antarctica
Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...
and
Greenland
Greenland is an autonomous territory in the Danish Realm, Kingdom of Denmark. It is by far the largest geographically of three constituent parts of the kingdom; the other two are metropolitan Denmark and the Faroe Islands. Citizens of Greenlan ...
. Berg winds blow off the African escarpment in response to large-scale weather systems in the
South Atlantic Ocean
The Atlantic Ocean is the second largest of the world's five borders of the oceans, oceanic divisions, with an area of about . It covers approximately 17% of Earth#Surface, Earth's surface and about 24% of its water surface area. During the ...
, the African interior, and the
Southern Indian Ocean.
Coastal lows and berg winds

Berg winds are usually accompanied by coastal lows.
These coastal lows owe their existence to the configuration of the plateau, escarpment and coastal plain (see diagram on the right, above), in that they are confined to the coastal areas, always below the escarpment. Though they can arise almost anywhere along the coast, they often first appear on the west coast, or even on the
Namibian coast. They are then always propagated counter-clockwise along South Africa's coastline at between , from the west coast southwards to the
Cape Peninsula
The Cape Peninsula () of South Africa is a generally mountainous peninsula that juts out into the Atlantic Ocean at the south-western extremity of the African continent. At the southern end of the peninsula are Cape Point and the Cape of Good ...
and then eastward along the south coast, and finally north-eastward along the
KwaZulu-Natal
KwaZulu-Natal (, also referred to as KZN) is a Provinces of South Africa, province of South Africa that was created in 1994 when the government merged the Zulu people, Zulu bantustan of KwaZulu ("Place of the Zulu" in Zulu language, Zulu) and ...
coastline, to finally dissipate north of Durban, due to the divergence of the coastline from the plateau which disappears altogether in the vicinity of the
Limpopo valley.
[ ] There is always a hot off-shore berg wind ahead of a coastal low, which can blow for several days or for only for a few hours. This is then followed by cool onshore winds which bring low cloud, fog or drizzle to the region, but may, on occasions, produce substantial precipitation when coupled to an approaching
cold front
A cold front is the leading edge of a cooler mass of air at ground level that replaces a warmer mass of air and lies within a pronounced surface Trough (meteorology), trough of Low-pressure area, low pressure. It often forms behind an extratropica ...
.
Coastal lows are a common feature of the coastal weather in South Africa with an average of about five lows of varying intensities passing through Port Elizabeth per month.
They are shallow (not more than deep), mesoscale (medium-sized) systems that are generally not more than across, trapped on the coastal plain by the escarpment on the inland side,
Coriolis effect
In physics, the Coriolis force is a pseudo force that acts on objects in motion within a frame of reference that rotates with respect to an inertial frame. In a reference frame with clockwise rotation, the force acts to the left of the moti ...
s on the oceanic side, and an inversion layer above. The pressure minima of these systems lie just off-shore.
In the south-west corner of the country the coastal lows are bounded on the inland side by the
Cape Fold Mountains
The Cape Fold Belt (CFB) is a long fold-and-thrust mountain belt along the western and southern coastlines of Western Cape, South Africa. The Cape Fold Belt formed during the Permian period (300 to 250million years ago) in the late Paleozoic ...
,
which tend to have a higher elevation than the escarpment, and form an almost continuous mountain barrier running parallel to the coast from the
Cederberg
The Cederberg mountains are located near Clanwilliam, Western Cape, Clanwilliam, approximately 300 km north of Cape Town, South Africa at about . The mountain range is named after the endangered Clanwilliam cedar (''Widdringtonia cedarbe ...
, to the north of
Cape Town
Cape Town is the legislature, legislative capital city, capital of South Africa. It is the country's oldest city and the seat of the Parliament of South Africa. Cape Town is the country's List of municipalities in South Africa, second-largest ...
, to
Cape Hangklip
Pringle Bay () is a small, coastal village in the Overberg region of the Western Cape, in South Africa. It is situated at the foot of Hangklip, on the opposite side of False Bay from Cape Point. The town and surrounds are part of the Kogelberg Bio ...
on the east side of
False Bay
False Bay (Afrikaans: ''Valsbaai'') is a body of water in the Atlantic Ocean between the mountainous Cape Peninsula and the Hottentots Holland Mountains in the extreme south-west of South Africa. The mouth of the bay faces south and is demarc ...
and then eastwards for to
Port Elizabeth
Gqeberha ( , ), formerly named Port Elizabeth, and colloquially referred to as P.E., is a major seaport and the most populous city in the Eastern Cape province of South Africa. It is the seat of the Nelson Mandela Bay Metropolitan Municipal ...
, where they eventually peter out (see the map above).
Origin of coastal lows

Coastal lows are initiated by the interaction of large scale weather systems such as the quasi-permanent
South Atlantic
The Atlantic Ocean is the second largest of the world's five oceanic divisions, with an area of about . It covers approximately 17% of Earth's surface and about 24% of its water surface area. During the Age of Discovery, it was known for ...
and
South Indian Ocean Anticyclone
A high-pressure area, high, or anticyclone, is an area near the surface of a planet where the atmospheric pressure is greater than the pressure in the surrounding regions. Highs are middle-scale meteorological features that result from interpl ...
s (high-pressure systems), the
cold front
A cold front is the leading edge of a cooler mass of air at ground level that replaces a warmer mass of air and lies within a pronounced surface Trough (meteorology), trough of Low-pressure area, low pressure. It often forms behind an extratropica ...
s that approach the subcontinent from the
South Atlantic Ocean
The Atlantic Ocean is the second largest of the world's five borders of the oceans, oceanic divisions, with an area of about . It covers approximately 17% of Earth#Surface, Earth's surface and about 24% of its water surface area. During the ...
, as well as the pressure systems on the plateau, causing air that has been warmed on the plateau by 2–3 days of sunny weather to flow down the Great Escarpment on to the coastal plain either on the west or south coasts of the country (i.e. causing a berg wind). The descending air warms up adiabatically, heating up the coastal plain, while, at the same time, causing an off-shore wind which blows the surface water away from the land to be replaced by cold water which wells up from the depths. This
upwelling of cold subsurface water from the ocean increases the ocean-land temperature difference, causing an on-shore wind.
The on-shore airflow is strengthened by the fact that the berg wind is not only hot, but it is also “stretched” vertically due to the sudden lowering of the floor over which it moves below the escarpment. Its low density, therefore, lowers the atmospheric pressure on the coast.
This low-pressure area caused by the berg wind draws the dense moist maritime air onshore to the right of the off-shore berg wind. Shear forces between these on- and off-shore winds on the right-hand side of the berg wind tend to cause clockwise (or
cyclonic) rotation of the air in this region. In addition, on reaching the escarpment the maritime air curves to the right round the low-pressure zone due to
Coriolis forces (in the southern hemisphere) accentuating the cyclonic circulation of the "coastal low".
The entire system is capped by an inversion consisting of a layer of warm air that has moved horizontally off the plateau at the level of the upper edge of the escarpment.
This inversion layer prevents the upwardly spiraling cyclonic air of the coastal low from rising above 1000–1500 m, thus preventing it from causing significant precipitation.
The weather associated with a coastal low
Along the south coast the passage of a coastal low is typically preceded by a north-easterly wind driven by the South Indian Ocean Anticyclone. The wind then backs quickly through northerly to north-westerly as its temperature rises. This is the berg wind phase of the coastal low. The wind then changes abruptly to a strong, cold, south or south-westerly wind (called a “buster” if the change in wind speed is greater than 35 km/h). The buster coincides with the passage of the pressure minimum. The onshore wind gradually diminishes in intensity during the course of about a day, and is associated with cloudy, misty or drizzly weather.
Because of the often abrupt changes in horizontal and vertical wind speeds and direction that can occur within these small weather systems they represent a significant hazard to aircraft on landing and taking off. During the climb-out and approach phases of flight, aircraft airspeed and height are near critical values, thus rendering the aircraft especially susceptible to the adverse effects of these wind shears.
The Atlantic
cold front
A cold front is the leading edge of a cooler mass of air at ground level that replaces a warmer mass of air and lies within a pronounced surface Trough (meteorology), trough of Low-pressure area, low pressure. It often forms behind an extratropica ...
s that move into and across the subcontinent, especially during the cooler months of the year, are frequently associated, the day before, by a coastal low that moves ahead of the front. Under these circumstances the southerly or south-westerly onshore wind of the coastal low gradually diminishes in intensity over the course of 12–20 hours, when it is replaced by a westerly wind (which may temporarily reach buster proportions) and a further drop in temperature accompanied by rain, indicative of the passage of the cold front.
Thus, particularly in
Cape Town
Cape Town is the legislature, legislative capital city, capital of South Africa. It is the country's oldest city and the seat of the Parliament of South Africa. Cape Town is the country's List of municipalities in South Africa, second-largest ...
, an obvious berg wind is generally regarded as a harbinger of cold, wet weather.
Other orographically trapped weather systems
Coastal lows are
orographic
Orography is the study of the topographic relief of mountains, and can more broadly include hills, and any part of a region's elevated terrain. Orography (also known as ''oreography'', ''orology,'' or ''oreology'') falls within the broader disc ...
ally trapped weather systems that also occur in other parts of the world, where there are mountain ranges between in length. Thus they occur along the coast of
Chile
Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...
, eastern
Australia
Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
and the west coast of North America, as well as on the eastern side of the
Appalachian Mountains
The Appalachian Mountains, often called the Appalachians, are a mountain range in eastern to northeastern North America. The term "Appalachian" refers to several different regions associated with the mountain range, and its surrounding terrain ...
of the United States. In each of these cases the weather systems are trapped vertically by
stable stratifications, and laterally by Coriolis effects against the mountains.
However, only the South African and the South American coastal disturbances are “coastal lows”; the remainder are generally produced by coastal
ridging.
See also
*
Foehn wind
*
Chinook wind
Chinook winds, or simply Chinooks, are two types of prevailing warm, generally westerly winds in western North America: Coastal Chinooks and interior Chinooks. The coastal Chinooks are persistent seasonal, wet, southwesterly winds blowing in from ...
*
Sirocco
Sirocco ( ) or scirocco is a Mediterranean wind that comes from the Sahara and can reach hurricane speeds in North Africa and Southern Europe, especially during the summer season.
Names
''Sirocco'' derives from '' šurūq'' (), verbal noun o ...
*
Bora (wind)
*
Diablo wind
Diablo wind is a name that has been occasionally used for the hot, dry 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 ...
*
Norte (wind)
The Norte is a strong cold wind which blows from the northeast in Mexico along the Gulf of Mexico. It primarily affects the states along the Coast, including: Tamaulipas, Veracruz, Tabasco, Campeche, and Yucatán.
Unlike El Nino
EL, El or el may ...
*
Katabatic wind
A katabatic wind (named ) is a downslope wind caused by the flow of an elevated, high-density air mass into a lower-density air mass below under the force of gravity. The spelling catabatic is also used. Since air density is strongly dependent o ...
*
Khamsin
*
Oroshi
*
Australian foehn winds
References
{{reflist
Winds
Geography of South Africa
Afrikaans words and phrases