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British Isles The British Isles are a group of islands in the North Atlantic Ocean off the north-western coast of continental Europe, consisting of the islands of Great Britain, Ireland, the Isle of Man, the Inner and Outer Hebrides, the Northern Isl ...
are an archipelago off the northwest coast of Europe, consisting of the islands of
Great Britain Great Britain is an island in the North Atlantic Ocean off the northwest coast of continental Europe. With an area of , it is the largest of the British Isles, the largest European island and the ninth-largest island in the world. It is ...
and
Ireland Ireland ( ; ga, Éire ; Ulster-Scots: ) is an island in the North Atlantic Ocean, in north-western Europe. It is separated from Great Britain to its east by the North Channel, the Irish Sea, and St George's Channel. Ireland is the s ...
along with smaller surrounding ones. Its position allows dry continental air from
Eurasia Eurasia (, ) is the largest continental area on Earth, comprising all of Europe and Asia. Primarily in the Northern and Eastern Hemispheres, it spans from the British Isles and the Iberian Peninsula in the west to the Japanese archipelago ...
to meet wetter air from the
Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the "Old World" of Africa, Europe ...
, which causes the weather to be highly variable, often changing many times during the day. It is defined as a temperate oceanic climate, or Cfb on the Köppen climate classification system. It is significantly warmer than other regions on the same latitude, previously thought to be due to the warmth provided by the
Gulf Stream The Gulf Stream, together with its northern extension the North Atlantic Drift, is a warm and swift Atlantic ocean current that originates in the Gulf of Mexico and flows through the Straits of Florida and up the eastern coastline of the Unit ...
; however, this has been disproven, and most of the mild temperatures have been linked to the Rocky Mountains and the heat storing capabilities of the North Atlantic Ocean. Temperatures do not often switch between great extremes, with warm summers and mild winters.


Temperature

The British Isles undergo very small temperature variations. This is due to its proximity to the Atlantic, which acts as a temperature buffer, warming the Isles in winter and cooling them in summer. Coastal areas tend to be more temperate than inland areas, as the influence of the ocean is less acute. Valleys can be especially cold, as cool air collects in them during the winter. July is usually the warmest month, with the highest temperatures being found closest to
Continental Europe Continental Europe or mainland Europe is the contiguous continent of Europe, excluding its surrounding islands. It can also be referred to ambiguously as the European continent, – which can conversely mean the whole of Europe – and, by ...
, in south-east England.


Sunshine and cloud

The sunniest times are the months of May and June, whereas December has the least sunshine. The clearest skies in the British Isles occur over the south of England, due to the winds from the continent. Equally, mountainous areas, especially in the North-west receive barely any sunshine, sometimes less than 1000 hours a year. In winter on north-south valleys there are sometimes only a few hours of sunshine in a day. Radiation fog may develop over inland areas of
Great Britain Great Britain is an island in the North Atlantic Ocean off the northwest coast of continental Europe. With an area of , it is the largest of the British Isles, the largest European island and the ninth-largest island in the world. It is ...
and can persist for hours or even days in the winter and can pose a major hazard for drivers and aircraft. Fog is more common inland and on higher altitudes; mainly during winter and during the morning at times of high pressure. On occasions blocking anticyclones (
high pressure systems 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 ...
) may move over the British Isles, which can persist for weeks or even months. The subsided, dry air often results in clear skies and few clouds, bringing
frost Frost is a thin layer of ice on a solid surface, which forms from water vapor in an above- freezing atmosphere coming in contact with a solid surface whose temperature is below freezing, and resulting in a phase change from water vapor (a ga ...
y nights in winter and hot days in the summer, when some coastal areas can achieve almost maximum possible sunshine for periods of weeks.


Precipitation

Rainfall varies across the Isles, with a general trend to more rain as you go west and in higher elevations. December and January are usually the wettest months. The
mountain range A mountain range or hill range is a series of mountains or hills arranged in a line and connected by high ground. A mountain system or mountain belt is a group of mountain ranges with similarity in form, structure, and alignment that have aris ...
s are the wettest areas in the U.K. These are some of the wettest locations in Britain. Most rainfall comes from North Atlantic depressions occur throughout the year and are particularly frequent and intense in the autumn and winter. They can on occasions bring prolonged periods of heavy rain, and
flood A flood is an overflow of water ( or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are an area of study of the discipline hydrolog ...
ing is quite common.
Snow Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water throughout ...
can occur during winter months, most frequently occurring during January and February.
Hail Hail is a form of solid precipitation. It is distinct from ice pellets (American English "sleet"), though the two are often confused. It consists of balls or irregular lumps of ice, each of which is called a hailstone. Ice pellets generally fal ...
is relatively common, and is most common during the summer months. Each of the United Kingdom's 50 strongest hailstorms on record since 1650 have occurred between the months of May and September.


Winds

The prevailing winds over the British Isles are from the south-west, and winds are strongest on coasts that face the Atlantic. Generally, the coast tends to be windier than inland areas; and the west tends to be windier than the east.
Gale A gale is a strong wind; the word is typically used as a descriptor in nautical contexts. The U.S. National Weather Service defines a gale as sustained surface winds moving at a speed of between 34 and 47 knots (, or ).Hebrides The Hebrides (; gd, Innse Gall, ; non, Suðreyjar, "southern isles") are an archipelago off the west coast of the Scottish mainland. The islands fall into two main groups, based on their proximity to the mainland: the Inner and Outer Hebr ...
experience on average 35 days of gale a year (a day where there are gale-force winds). Areas of high
elevation The elevation of a geographic location is its height above or below a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface (see Geodetic datum § V ...
tend to have higher wind speeds than low elevations.


Severe weather

The British Isles do not experience
extreme weather Extreme weather or extreme climate events includes unexpected, unusual, severe, or unseasonal weather; weather at the extremes of the historical distribution—the range that has been seen in the past. Often, extreme events are based on a locat ...
regularly. There have been several occasions where extreme weather events have occurred. In the winter of 1982, for a few days parts of central and southern England experienced temperatures lower than
central Europe Central Europe is an area of Europe between Western Europe and Eastern Europe, based on a common historical, social and cultural identity. The Thirty Years' War (1618–1648) between Catholicism and Protestantism significantly shaped the ar ...
and
Moscow Moscow ( , US chiefly ; rus, links=no, Москва, r=Moskva, p=mɐskˈva, a=Москва.ogg) is the capital and largest city of Russia. The city stands on the Moskva River in Central Russia, with a population estimated at 13.0 millio ...
. In contrast, the summers of 1975 and 1976 experienced temperatures as high as . It was so dry the country suffered drought and water shortages. Extended periods of extreme weather, such as the drought of 1975–1976 and the very cold winters of 1946–1947, 1962–1963, 1978–79, 1981–1982 and 2009–2010, are often caused by blocking
anticyclone An anticyclone is a weather phenomenon defined as a large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere as viewed from abov ...
s which can persist several days or even weeks. In winter they can bring long periods of cold dry weather and in summer long periods of hot dry weather.


Cyclones

Tropical cyclone A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Dep ...
s themselves do not affect the British Isles due to the cold temperature of the surrounding ocean. Any tropical cyclone that comes near the Isles has said to have undergone a process called
extratropical transition Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are low-pressure areas which, along with the anticyclones of high-pressure areas, drive the weather over much of the Earth. Extratropical cyclones are capable of p ...
. The Isles do experience these
extratropical cyclone Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are low-pressure areas which, along with the anticyclones of high-pressure areas, drive the weather over much of the Earth. Extratropical cyclones are capable of ...
s, the Great Storm of 1987 was a deep depression which formed in the
Bay of Biscay The Bay of Biscay (), known in Spain as the Gulf of Biscay ( es, Golfo de Vizcaya, eu, Bizkaiko Golkoa), and in France and some border regions as the Gulf of Gascony (french: Golfe de Gascogne, oc, Golf de Gasconha, br, Pleg-mor Gwaskogn), ...
, which also contained the remnants of
Hurricane Floyd Hurricane Floyd was a very powerful Cape Verde hurricane which struck the Bahamas and the East Coast of the United States. It was the sixth named storm, fourth hurricane, and third major hurricane in the 1999 Atlantic hurricane season. Floyd ...
. Hurricane Lili of 1996 and Hurricane Gordon of 2006 both were strong
extratropical cyclones Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are low-pressure areas which, along with the anticyclones of high-pressure areas, drive the weather over much of the Earth. Extratropical cyclones are capable of p ...
with tropical storm-force winds, which caused transport closures, power-cuts and flooding. In 2011, the remnants of Hurricane Katia brought near hurricane-force winds to Scotland, with sustained winds reaching while centred over the
Isle of Lewis The Isle of Lewis ( gd, Eilean Leòdhais) or simply Lewis ( gd, Leòdhas, ) is the northern part of Lewis and Harris, the largest island of the Western Isles or Outer Hebrides archipelago in Scotland. The two parts are frequently referred to as ...
. In 2017, Hurricane Ophelia brought severe storms to Ireland, and carried
Saharan dust Saharan dust is an aeolian mineral dust from the Sahara desert, the largest hot desert in the world. The desert spans just over 9 million square kilometers, from the Atlantic Ocean to the Red Sea, from the Mediterranean sea to the Niger River v ...
and smoke from wildfires in Portugal into the atmosphere over the United Kingdom, creating red and orange skies across the country.


Thunderstorms

Thunderstorm A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorms are somet ...
s are most common in London, the South-East, east of England, the East Midlands, and least common in the North-West. Greater London, Kent, Sussex, Essex, Hertfordshire, Cambridgeshire, Suffolk and Norfolk are the regions with the most thunderstorms during the year. The South-West and the West Midlands also get storms but usually less severe. Occasionally, thunderstorms can be severe and produce large
hail Hail is a form of solid precipitation. It is distinct from ice pellets (American English "sleet"), though the two are often confused. It consists of balls or irregular lumps of ice, each of which is called a hailstone. Ice pellets generally fal ...
stones as seen in
Ottery St Mary Ottery St Mary, known as "Ottery", is a town and civil parish in the East Devon district of Devon, England, on the River Otter, about east of Exeter on the B3174. At the 2001 census, the parish, which includes the villages of Metcombe, Fair ...
,
Devon Devon ( , historically known as Devonshire , ) is a ceremonial and non-metropolitan county in South West England. The most populous settlement in Devon is the city of Plymouth, followed by Devon's county town, the city of Exeter. Devon i ...
in October 2008, where drifts reached .


Climate change

Estimates produced by the
Met Office The Meteorological Office, abbreviated as the Met Office, is the United Kingdom's national weather service. It is an executive agency and trading fund of the Department for Business, Energy and Industrial Strategy and is led by CEO Penelope ...
predict average annual temperature to increase by 2 °C (4 °F) and the warmest summer day to increase by 3 °C (6 °F) by the 2050s. Average winter rainfall is also likely to increase and most areas will see a slight decrease in annual rainfall.


Recent events

In the early 21st century, the British Isles have undergone some record breaking events. In 2004-2006, a partial drought caused fires to break out throughout the south of Great Britain, and water restrictions were introduced in some areas. The drought problems were solved due to the unusually wet period between October 2006 and July 2007, which had higher than average rainfall. The year 2006 was an unusually warm one. Although the year started off cool, from April the weather stayed warmer than average. July was the hottest month on record for the United Kingdom.


See also

*
Climate of the United Kingdom The United Kingdom straddles the higher mid-latitudes between 49° and 61°N on the western seaboard of Europe. Since the UK is always in or close to the path of the polar front jet stream, frequent changes in pressure and unsettled weather ar ...
* Climate of Ireland


References

{{reflist British Isles
British Isles The British Isles are a group of islands in the North Atlantic Ocean off the north-western coast of continental Europe, consisting of the islands of Great Britain, Ireland, the Isle of Man, the Inner and Outer Hebrides, the Northern Isl ...
Climate of the United Kingdom Climate of Ireland