The Weather Observing and recording Powerpoint Presentation © Pitsford Hall weather station Northamptonshire Grammar School Abridged version without video clips

What is weather? Weather describes the state of the atmosphere at any particular time. Weather can be described in terms of temperature, precipitation (snow, rain & hail), wind speed and direction, visibility and cloud amounts.

What is Climate? Climate describes the average weather of a particular part of the world at different times of the year In Britain we would expect cool summers and mild winters with moderate rainfall throughout the year

The Weather Station A weather station makes continuous measurements of different aspects of the weather. Weather stations use standard instruments so that their readings can be compared.

HOWEVER… You can make weather measurements with equipment a lot cheaper and simpler than the kit shown on the previous slide which is an official Met Office station. Please see for more information.

Temperature Temperature is recorded using thermometers housed inside a Stevenson screen Weather stations record both air temperature and the temperature of the ground

Temperature: The Stevenson Screen Why is the screen painted white? Why is it raised on legs above the ground? Why has it got louvred sides?

Precipitation Rainfall, snow, hail and fog. Rainfall is measured in a raingauge. Some raingauges record rainfall automatically whilst others are emptied everyday by an observer

Wind The direction and strength of the wind are both measured A wind vane measures direction An anemometer records strength Wind strength can also be measured using the Beaufort Scale

The Beaufort Scale

Pressure Pressure is the weight of the atmosphere When air rises pressure falls When air sinks pressure increases Pressure controls the type of weather Barometers and barographs record pressure

Recording pressure

Sunshine A note is made of the number of hours of bright sunshine each day Sunshine is traditionally measured using a Campbell-Stokes sunshine recorder

Cloud The amount of the sky obscured by cloud Different types of clouds Sometimes even the speed and direction in which the clouds are moving are recorded using a nephoscope

Cloud Types - Cumulonimbus

Cloud Types - Cumulus

Cloud Types - Stratus

Cloud Types - Cirrus

Britain’s Weather The Seasons

Temperature In summer it gets warmer the further south you go In winter it gets warmer the further west you go In Britain temperature is affected by latitude and the sea

Temperature: Latitude

Temperature: Summer & Winter In winter the northern hemisphere is tilted away from the sun so the sun’s rays are weaker In summer the northern hemisphere is tilted towards the sun so the sun’s rays are stronger

Temperature: Summer & Winter During the course of the year the Earth tilts towards and away from the sun The mid-points of this cycle are called the equinoxes (spring and autumn)

Temperature: The Sea The North Atlantic Drift is a warm ocean current originating in the Caribbean It moves across the Atlantic keeping the west of Britain warmer than the east in winter

Winter in Canada & Britain

Rainfall In Britain it rains the most in the west and in mountainous areas Rain is brought across Britain from weather systems called depressions In summer showers result from convection on warm days

How it rains The surface is heated by the sun Air rises Air expands and cools Air condenses Water droplets grow to form raindrops Air can rise in different ways

Relief rainfall

Cyclonic Rainfall Depressions are areas of low pressure formed when cold and warm air meet The warm air rises above the cold air to form a front There are two types of fronts depending on the way in which the air masses are moving.

Cyclonic Rainfall: Fronts Warm fronts form where warm air moves towards cold air Cold fronts form where cold air moves towards warm air As air rises at fronts both are responsible for rain

Convectional rainfall Common on hot summer days inland Hot air rises quickly and condenses to form cumulonimbus Water freezes at the top of the cloud forming hail Associated with lightning

Fair Weather Fair weather is produced by high pressure High pressure forms anticyclones Air sinks and prevents the formation of rain clouds Anticyclones cause heatwaves in summer and frosty/foggy mornings in winter

Forecasting the Weather Modern forecasts use computers to simulate the likely weather based on careful observations from 100s of weather stations round the world Satellite images and radar give a better picture of the weather over a wide area

A Satellite Image

A Radar Image Cyclonic rainfall moving in from the west The brighter the colour, the heavier the rainfall Mountains intensify the rain such as over the Scottish Highlands

The Weather Map Weather maps summarise the weather over a wide area using symbols What symbols are used for: pressure, wind direction & strength, cloud cover and rainfall?

Weather This Powerpoint presentation was produced specially for the Department of Geography & Geology at Northamptonshire Grammar School May 2005 © M J Lewis