Temperature and Precipitation in the UK

The UK has one of the most variable weather patterns in the world, in one day you may experience rain, snow, thunder and lightning, hail and warm sunshine. There are several influences that give Britain such variable weather, a Northern latitude, close proximity to the Atlantic Ocean and the directional flow of the Gulf Stream all have a massive influence on the climate (temperature/precipitation) that the UK experiences during a year.

Temperature
The UK is a temperate region with average temperatures of 7-11º C, the temperature varies throughout the year but the range is small (approximately 12º C) compared to temp variations in other places.

Largely its latitude influences the temperature of the UK; it lies in the Northern Hemisphere 50-60 degrees north of the equator and it subject to constant changes in solar radiation levels. When the Northern Hemisphere is facing towards sun, the UK experiences summer, the winter occurs when the Northern Hemisphere is facing away from the sun.

During winter in the UK the sun sits low in the sky because the earths tilt causes it to be farther away from the direct energy being radiated towards the equatorial regions. This tilt also means that the hours of daylight are reduced from those of the summer months and so its effects are weaker still.

The winter season is experienced differently throughout the UK with varying degrees of temperature change, the average temperatures in England and Wales are about 4,4º C, Scotland being further north has lower winter temperatures with averages of 3º C.

The reduced hours of daylight that come with the Britain’s winter position also contribute to lower temperatures, the land does not have as long to absorb heat during the day leading to cold nights and mornings, the further north you travel lesser hours of light are experienced, this contributes to Scotland’s cooler winter temperatures.

The UK experiences a temperature ‘lag’ due to it being a small island and surrounded by water, as water stores energy for longer than land the water surrounding the UK keeps the temperature up in winter, the overall temperature of the UK is generally higher than other inland European countries on similar latitudes.

Variations in temperature occur because of the effects of warming ocean and air currents that have travelled through the Atlantic Ocean having originated in the Gulf of Mexico. These warm waters raise the temperature around north and Western Europe. The UK receives warm air and water from the North Atlantic drift from the west, warming the UK by 5-8º C; this gives the west and southwest coasts warmer winter temperatures than would be expected at this latitude. The east coasts of Britain during winter is a good few degrees colder on average than the west, the eastern temperature is more reflective of temperatures experienced in inland Europe.

January on average is the coldest month, the ocean has time to cool down during the previous autumn/winter months and has very little warming influence; temperatures drop to an average of 2-3º C.

As the earth continues on its obit the northern hemisphere starts to turn towards the sun, this increases day length and brings the UK into a more direct path of the suns rays. The sun gets higher in the sky and days get gradually longer so the land has a longer time to heat and is absorbing/radiating more heat.

Summer in the UK can be variable and quite unpredictable a lot of the time. Everything that occurs during the winter months is flipped for the summer, the tilt of the earth means that the UK is getting plenty of solar energy and the waters are gradually warming up, average temperatures are about 15.6º C but can sometimes reach heights of 32º C.

The tilt also gives different areas of Britain different amounts of solar energy, The southeast gets more intense heat for longer periods and so the average temperature is much higher than that of northwest, which is receiving less energy per day. Temperatures in the southwest average at 17º C compared to 14º C for Northwest Britain.

The summer months bring strong solar rays, these rays have the dominant effect on temperature in Britain but the Atlantic Ocean still contributes to the overall temperature by bring cooler water and air to the waters surrounding Britain. The cooler waters bring the land temperature down and create weather patterns along the coast. Inland Britain remains higher in temp and is only very mildly influenced by the cooling effects of the ocean.

The ocean has a regulating and cooling effect on annual coastal temperatures compared to inland temperatures, this is especially so for areas directly influenced by the effects of the Gulf Stream. Temperatures in the west and southwest have a smaller temperature range and don’t experience the highest and lowest temperatures.


Precipitation
Precipitation in Britain is closely linked with temperature and temperature changes from season to season. It is also influenced by geography and altitude. The whole of Britain experiences regular rainfall with dry areas experiencing 150 days of rain and wet areas 200 days, the difference between the wet and dry areas is the quantity and across the UK there is a wide range of rainfall volumes.

During winter the precipitation across Britain varies, the land is cool but water in the ocean still stores some heat. Areas closer to abundant water will experience more precipitation than inland areas. The warmer waters brought in by ocean currents causes evaporation to occur when it meets with cooler waters immediately round the island.

The warm waters reach Britain on the west and so the most noticeable changes occur here, air is forced to rise when confronted by a coastal mountain barrier and then reaches the colder higher landforms. Once the evaporated water reaches cooler land its temp drops and the water condenses and forms precipitation. The precipitation falls more on coastal areas in the west and northwest where temp change is largest.

Much of the precipitation in Britain is caused by depressions where cold and warm air meet, these start out in the ocean and move northeast across the Atlantic, these depressions pass over west Britain with the warmer fronts travelling north. These frontal depression cause increased levels of rainfall across the west and northwest coast.

The highlands of Britain are subject to higher levels of rainfall because of the altitude, as warm air is blown in and hits he colder airs surrounding landforms at higher altitude the temperature change is rapid and large causing large quantities of precipitation to be deposited over these areas. The western highlands of Scotland can experience over 3000mm of rain annually, where as the Scottish east coat can have just 800mm. The lowlands of Britain have much less rainfall, with some southeast inland areas having as little as 500mm of rain a year, this is often because the cold temperatures and high altitudes of the western highlands have caused most of the moisture to be lost before the air passes over the east.

The air coming into lowland South and southeast Britain has travelled over land in Europe and much less water so the air is cold and dry, the colder dryer air coming in form more stable weather pattern and reduced amounts of precipitation. Most of this area is in a rain-shadow from highland Britain and so this reduces the amounts of precipitation more so.

During summer the overall precipitation of the UK is reduced but is still subject to varying amounts of rainfall. The increased temperatures over the land mean that cool air brought in from the surrounding air and water currents is more stable with less cloud formation. However, British precipitation can be very unpredictable and there are periods of heavy rain often with thunderstorms during the summer months.

The land gets incredibly warm during the summer especially in areas of lowland Britain that are not so influenced by the cooling presence of the ocean currents. The heat of the land forces the air up, through air that is cooler; this convection heating causes unstable air movement and eventually it cools forming large cumulo-nimbus clouds which are notorious rain and thunder clouds.


Reference:
http://www.metoffice.gov.uk/education/secondary/students/bi_climate.html