When the water droplets or ice crystals in clouds grow to a certain size, gravity causes them to fall because of their own weight. Relief rainfall is a dominant method of precipitation formation in the UK and relates to the precipitation that is created as air masses are pushed up and over mountainous or upland areas. Relief rainfall occurs where moist air is forced to rise over a physical barrier such as a mountain range.
Warm air is carried to the West coast of Britain by our prevailing dominant winds, the South Westerlies. This air encounters the high land on the coast of Ireland , then the Lake District and the Pennines and it is forced to rise above this barrier.
As it rises, the warm air cools with height at a rate of 9. As the air cools water vapour condenses to form clouds and eventually it rains over Britain 's highland areas. Rainfall in Wales varies widely, with the highest average annual totals being recorded in the mountainous areas of Snowdonia, with the wettest parts having over 3, mm per year, and the Brecon Beacons, where the yearly fall is comparable to the English Lake District or the Western Highlands of Scotland.
In the east, close to the border with England, annual totals are similar to those over much of the English Midlands around 1, mm per year , whilst similar totals are also found in the coastal areas.
Throughout Wales, the months of October to January are significantly wetter than those from February to September, unlike places in south-east Scotland and the English Midlands where July and August are often the wettest months of the year.
This is a reflection of the relatively low frequency of thunderstorms in Wales compared with England. For example at Cardiff, thunder occurs on an average of 11 days a year, compared with in many places in England.
In the west and north-west, the frequency declines to around eight days per year. Snow is comparatively rare near sea level in Wales but much more frequent over the hills.
The average number of days each year when sleet or snow falls in Wales varies from about 10 or less in some south-western coastal areas to over 40 in Snowdonia. Snow rarely lies on the ground near sea level before December or after March, and the average number of days with snow lying in Wales varies from six or less around the coasts to over 30 in Snowdonia.
Even places near the coast experienced prolonged snow cover during these two winters. In heavy snowfalls there can be quite extensive drifting of snow in strong winds, especially over higher ground, resulting in severe dislocation of transport.
Fortunately, such occasions are rare, but one of the worst snowstorms in the 20th century in South Wales occurred on 7 and 8 January , when depths of one metre or more were commonplace, with severe drifting and power lines brought down. The strongest winds in the British Isles are associated with the passage of deep depressions across or close to the country. These are most frequent in winter and it is then that gales are most frequent. As these depressions are most intense over the open Atlantic Ocean, low-lying parts of Wales have more-frequent gales.
For example, in the extreme south-west of Dyfed about 30 days of gales occur on average per year. Further north, Wales is more protected by Ireland.
Other coastal areas have 15 days or more of gale with the number of days decreasing to five days or fewer inland. In general, wind speed increases with height, with strongest winds being observed over the summits of hills and mountains.
There are no wind recording stations at high altitudes in Wales, so no data can be given but, as an indication, Snaefell on the nearby Isle of Man at metres has, on average, over days of gales a year. Wales is generally cloudier than England as a result of the hilly nature of the terrain that forces up moist, maritime air moving in from the Atlantic.
Even so, the south-western coastal strip of Dyfed has an annual average of over 1, hours of sunshine — a total also achieved by many places on the south coast of England. The dullest parts of Wales are the mountainous areas, with average annual totals of less than 1, hours. Mean daily sunshine figures reach a maximum in May or June, and are at their lowest in December.
The key factor is the length of day throughout the year, but prevailing winds and cloud play their part as well. Visibility — Much of Wales enjoys excellent visibility. The traditional areas of heavy industry are close to the southern coast — a location that is, in itself, relatively breezy and free from serious reductions of visibility by reason of smoke.
Fog statistics are scarce but, given the mountainous nature of the country and the proximity to the sea, hill fog can be both extensive and frequent and is a potential hazard to be borne in mind by walkers in Snowdonia and the Brecon Beacons.
Temperature — over Northern Ireland the mean annual temperature at low altitudes varies from about 8. The mean annual temperature decreases by about 0. In winter, the temperatures of coastal areas are influenced by the surface of the surrounding sea.
Inland, the lowest temperatures are to be found, where cold air drains into the bottoms of valleys. The lowest temperature recorded in Northern Ireland was July is normally the warmest month in Northern Ireland, and the highest temperatures of all have occurred inland, furthest away from the cooling influence of the Atlantic.
The highest recorded temperature was Rainfall in Northern Ireland varies widely, with the highest annual average totals being recorded in the Sperrin, Antrim and Mourne Mountains where the yearly fall of around 1, mm is about half that of the English Lake District, or the western Highlands of Scotland. In the east, close to the coast, and near to the southern and eastern shores of Lough Neagh, the annual totals of just under mm are similar to those near the Firth of Forth in Scotland.
Generally, rainfall distribution is closely related to topography. The seasonal variation of rainfall in Northern Ireland is not large, but throughout the province the wettest months are between August and January, unlike places in south-east Scotland or in the English Midlands, where July and August are often the wettest months of the year.
This is partly a reflection of the relatively low frequency of thunderstorms in Northern Ireland, compared with that of England.
For example, at Armagh thunder occurs on an average of less than four days per year, compared with at many places in England. Only in a few places, mainly away from the coasts, does the frequency of thunder exceed five days per year.
Snow is comparatively rare near sea level in Northern Ireland, but much more frequent over the hills. The average number of days each year when sleet or snow falls in Northern Ireland varies from around 10 near the east coast to over 30 in the mountains of Sperrin, Antrim and Mourne.
Snow rarely lies on the ground at sea level before December or after March and the average annual number of days with snow lying in Northern Ireland varies from less than five around the coasts to over 30 in the mountains. With heavy snowfalls there can be quite extensive drifting of the snow in strong winds, especially over the higher ground, resulting in severe disruption of transport. Fortunately, such occasions are comparatively rare. These are most frequent during winter, which is when gales can occur on exposed western and northern coasts of both Britain and Ireland.
For example, the Hebrides experience on average about 35 days of gale a year, and the extreme south-west of England about In Northern Ireland, the coastal areas are not so exposed as these areas are afforded some protection both by the rest of Ireland and adjacent parts of Scotland.
Thus, the coastal areas of the counties of Antrim and Down have about 15 days of gale per year, while the number of days decreases inland to five or fewer. There are no wind recording stations at high altitudes in Northern Ireland, so no data can be given but, as an indication however, Snaefell on the nearby Isle of Man at metres averages over days of gale a year. On the whole, Northern Ireland is cloudier than England because of the hilly nature of the terrain and the proximity to the Atlantic.
Even so, the coastal strip of County Down manages an annual average total of over 1, hours of sunshine. This compares favourably with many coastal areas of England and Wales, though not with the 1, hours achieved in places along the south coast of England.
The dullest places in Northern Ireland are the more-mountainous areas, where the annual average falls below 1, hours. Any early morning mist or fog that might develop will usually clear rapidly, though it can be much more persistent during winter months. Given the hilly nature of the country and its relative proximity to the sea, hill fog can be both extensive and frequent and is a potential hazard to be borne in mind by walkers. Explain why Moscow, on a similar latitude to London, has warmer summers and colder winters than the English capital.
Outline the meaning of the following phrases: a. What is the correct value for the number of days with snow falling over the Cairngorms 40, 60, 80 or ? What is an urban heat island? What are the meteorological conditions that may favour its formation? Why do temperatures in the inland parts of the UK differ from those localities that are nearer the sea? Describe and explain the type of weather hazards which walkers might face in upland parts of the UK.
The highest recorded temperature in England was made at Brogdale near Faversham in Kent: a. Was it In which year did this occur , , or ? Web page reproduced with the kind permission of the Met Office. By clicking any link on this page you are giving your consent for us to set cookies. More info. Strictly Necessary Cookie should be enabled at all times so that we can save your preferences for cookie settings.
If you disable this cookie, we will not be able to save your preferences. This means that every time you visit this website you will need to enable or disable cookies again.
UK Climate. Contents 1. Additional UK climate information 5. Questions 1. The climate of a locality is mainly governed by the factors of: i latitude; ii location, relative to continents and oceans; iii situation in relation to large-scale atmospheric circulation patterns; iv altitude; v local geographical features, such as topography or the nature of the built-up area. The main characteristics of the British climate This session aims to look at the main characteristics of the climate of the British Isles.
Temperature: the south is warmer than the north. Precipitation over the British Isles is the result of one or more, of three basic mechanisms. Precipitation Rainfall Fig 1: Monthly averages of rainfall mm for a selection of stations in England. The maximum rainfall recorded in one day was mm at Martinstown Dorset on 18 July Snow Fig 2: year average number of days in month with snow lying at hours at selected stations.
Sunshine Fig 4: year average monthly duration of bright sunshine in hours for selected stations. Precipitation Rainfall Fig 5: Monthly averages of rainfall mm for a selection of stations in Scotland. Snow Fig 6: year average number of days in month with snow lying at hours at selected stations. Winds Fig 7: Monthly average number of days with gales in selected stations. Sunshine Fig 8: year average monthly duration of bright sunshine in hours for selected stations.
Precipitation Rainfall Fig 9: Monthly averages of rainfall mm for a selection of stations in Wales. Snow Fig year average number of days in month with snow lying at hours at selected stations.
Winds Fig Monthly average number of days with gales in selected stations. Sunshine Fig year average monthly duration of bright sunshine in hours for selected stations. Precipitation Rainfall Fig Monthly averages of rainfall mm for a selection of stations in Northern Ireland. The air mass is usually dry and stable but as it passes over part of the North Sea, sufficient heat and moisture can lead to the formation of showers, often snow, over eastern England and Scotland. During summer, the polar air mass brings warm air as even northern parts of Europe experience high temperatures during the summer months.
Tropical continental air reaches Britain from the Saharan region of Africa. It gives dry weather in the summer and also gives pleasantly warm weather in the winter. The general patterns of climate experienced in Britain have been identified. However, there are also noticeable differences that occur throughout Britain. The coldest winter temperatures in Britain occur in eastern Scotland and England.
The western side of Britain is warmed by the influence of the tropical maritime airstream. Temperatures are therefore colder in the east than in the west during winter.
During summer the south is warmer than the north. This is due to the differences in solar heat received, being greater in the south. The British climate can be divided into four parts as shown on the map below.
Home Africa N. America S. East Oceania. East Oceania All the countries. Climate - United Kingdom Average weather, temperature, rainfall, when to go, what to pack.
0コメント