A few questions answered....
What is the difference between weather and climate?
Climate is based on the long term averages for a particular place - usually calculated over a 30-year period or longer to iron out unusual years. Weather is simply the day-to-day changes and extremes we experience!
What is the difference between weather and climate?
Climate is based on the long term averages for a particular place - usually calculated over a 30-year period or longer to iron out unusual years. Weather is simply the day-to-day changes and extremes we experience!
How is temperature measured?
Air temperature is one of the most difficult elements of the weather to measure accurately. Ask five different people to place a thermometer outside to measure the temperature and you'll get five different readings! However, the standard way to measure temperature is to use a Stevenson Screen. This is an important piece of kit as it shields the instruments from rain and wind, and more importantly, the sunshine. It is double louvered, which allows a free-flow of air inside, and painted white to reflect the sun's heat.
The screen itself should be situated 2 metres above grass and in an open position. Some screens are small, some are large, but the Met Office uses specified designs so that temperatures around the UK (and world) can be compared. Using one of these ensures that temperature readings are not over-inflated during the day, as would happen if you just hung a thermometer in the garden. It also ensures readings aren't under reading on clear, starry nights! The picture above shows the inside of a my Met Office large-pattern screen, which houses the 4 thermometers needs to measure ambient, maximum and minimum temperatures - as well as humidity. Temperature is measured from 0900-0900GMT.
At the end of the month the mean temperature is calculated from the mean daily maximum and mean daily minimum temperatures for that month. This can then be compared with the long term normal.
Air temperature is one of the most difficult elements of the weather to measure accurately. Ask five different people to place a thermometer outside to measure the temperature and you'll get five different readings! However, the standard way to measure temperature is to use a Stevenson Screen. This is an important piece of kit as it shields the instruments from rain and wind, and more importantly, the sunshine. It is double louvered, which allows a free-flow of air inside, and painted white to reflect the sun's heat.
The screen itself should be situated 2 metres above grass and in an open position. Some screens are small, some are large, but the Met Office uses specified designs so that temperatures around the UK (and world) can be compared. Using one of these ensures that temperature readings are not over-inflated during the day, as would happen if you just hung a thermometer in the garden. It also ensures readings aren't under reading on clear, starry nights! The picture above shows the inside of a my Met Office large-pattern screen, which houses the 4 thermometers needs to measure ambient, maximum and minimum temperatures - as well as humidity. Temperature is measured from 0900-0900GMT.
At the end of the month the mean temperature is calculated from the mean daily maximum and mean daily minimum temperatures for that month. This can then be compared with the long term normal.
What are the UK extreme temperatures ever recorded?
Summer 2003 was a hot one, and the heatwave peaked in early August. A reading of 38.5C was recorded at Brogdale (Kent) on the 9th. The previous highest was 37.1C measured at Cheltenham (Gloucestershire) in August 1990.
The lowest measured air temperature has been recorded several times - most recently in December 1995, when the mercury dipped to -27.2C in Altnaharra (Highland) on the 30th. It had previously been recorded in Braemar (Grampion) back in January 1982 and February 1895.
At this station, a temperature of 34.3C was logged on 19th Jul 2006. The lowest was -12.0C in November 2010.
Summer 2003 was a hot one, and the heatwave peaked in early August. A reading of 38.5C was recorded at Brogdale (Kent) on the 9th. The previous highest was 37.1C measured at Cheltenham (Gloucestershire) in August 1990.
The lowest measured air temperature has been recorded several times - most recently in December 1995, when the mercury dipped to -27.2C in Altnaharra (Highland) on the 30th. It had previously been recorded in Braemar (Grampion) back in January 1982 and February 1895.
At this station, a temperature of 34.3C was logged on 19th Jul 2006. The lowest was -12.0C in November 2010.
AIR frost and GROUND frost - what's the difference?
On clear nights the ground cools much more quickly than the air. If the ground temperature dips below 0C (even by just 0.1C) then a ground frost is recorded - yet the air temperature as measured in the Stevenson Screen might be several degrees higher. Ground frosts are far more frequent that air frosts, and can be recorded at almost any time of the year. The only month never to have had a ground frost in Rosliston is July...but give it time! A thermometer placed over grass measures the lowest temperature overnight at ground level.
Ground frosts can be very slight - and very often go unnoticed. The ground may not necessarily be white-over like it can be in winter - but a temperature below freezing at ground level can still do a lot of damage to young plants in April or May.
An air frost is simply when the air temperature falls below freezing - but because the ground is always colder at night, it would give a ground frost as well. Air frosts are therefore much more severe and occur far less than ground frosts alone. The first air frosts of the season normally occur around October, and can be recorded as late as May.
On clear nights the ground cools much more quickly than the air. If the ground temperature dips below 0C (even by just 0.1C) then a ground frost is recorded - yet the air temperature as measured in the Stevenson Screen might be several degrees higher. Ground frosts are far more frequent that air frosts, and can be recorded at almost any time of the year. The only month never to have had a ground frost in Rosliston is July...but give it time! A thermometer placed over grass measures the lowest temperature overnight at ground level.
Ground frosts can be very slight - and very often go unnoticed. The ground may not necessarily be white-over like it can be in winter - but a temperature below freezing at ground level can still do a lot of damage to young plants in April or May.
An air frost is simply when the air temperature falls below freezing - but because the ground is always colder at night, it would give a ground frost as well. Air frosts are therefore much more severe and occur far less than ground frosts alone. The first air frosts of the season normally occur around October, and can be recorded as late as May.
What is 'wind chill'?
Wind chill is how cold the wind makes you feel - it's not the actual temperature. At a temperatures of +5C combined with a wind speed of 10mph, it would feel more like -10C. Wind is just air in motion and a thermometer would not detect the 'feel' of the wind like we can. The wind blows on our skin and evaporates moisture from it, thus cooling you down. The table above shows you how wind chill is calculated.
What is relavite humidity?
Relative humidity is how much moisture there is in the air around us, relative to the maximum amount it can hold. Warm air holds more water vapour than cold air, so 50% humidity at 10C would be much drier than 50% at 30C.
A wet and dry-bulb thermometer measures humidity accurately. The dry thermometer gives an ambient reading, whilst the wet-bulb gives a lower reading due to wet muslin being draped around its bulb. The moisture around the wet-bulb evaporates and cools the bulb as it does so. On dry days there can be as much as 10C difference between the two readings. These thermometers can be seen as the virtical pair in the picture further up the page. If both readings are identical at any temperature, we say the relative humidity is 100%.
Relative humidity is how much moisture there is in the air around us, relative to the maximum amount it can hold. Warm air holds more water vapour than cold air, so 50% humidity at 10C would be much drier than 50% at 30C.
A wet and dry-bulb thermometer measures humidity accurately. The dry thermometer gives an ambient reading, whilst the wet-bulb gives a lower reading due to wet muslin being draped around its bulb. The moisture around the wet-bulb evaporates and cools the bulb as it does so. On dry days there can be as much as 10C difference between the two readings. These thermometers can be seen as the virtical pair in the picture further up the page. If both readings are identical at any temperature, we say the relative humidity is 100%.
How is rainfall calculated?
Rainfall is measured in mm - to the nearest tenth. 1mm of rainfall is equivalent to one litre of water falling per square metre. A standard Met Office raingauge is 5 inches in diameter (the smaller one in the picture). The larger rainguages measure rainfall over a longer period, calculating the duration of the rainfall period.
Rainfall is measured every 24hrs from 0900-0900GMT, and totals are then calculated at the end of the month and compared against the long term average.
Rainfall is measured every 24hrs from 0900-0900GMT, and totals are then calculated at the end of the month and compared against the long term average.
How does the wind affect our weather?
Apart from making us feel cooler when it's windy, the direction of the wind is important to us here in the UK. Its direction will detarmine the sort of weather we get, and how warm it feels. Generally speaking, a southerly wind will bring much warmer weather than a northerly. Our prevailing win din the UK is south-westerly, which is why we're so often damp and rainy! Easterlies can be bitter in winter coming off a cold continent - but can bring us hot weather in summer, especially if they come from a drier south-easterly direction.
Apart from making us feel cooler when it's windy, the direction of the wind is important to us here in the UK. Its direction will detarmine the sort of weather we get, and how warm it feels. Generally speaking, a southerly wind will bring much warmer weather than a northerly. Our prevailing win din the UK is south-westerly, which is why we're so often damp and rainy! Easterlies can be bitter in winter coming off a cold continent - but can bring us hot weather in summer, especially if they come from a drier south-easterly direction.