Measuring the weather

Weather affects us in many ways. It affects what we do and what we wear, how we travel and even our moods. Meteorologists measure weather conditions in different places and use this information to report and make forecasts about future weather conditions. This is useful because people can be warned about hazardous weather conditions such as storms and floods.

What do we measure?

  • Temperature
  • Precipitation, eg rainfall
  • Wind speed and direction
  • Cloud cover and visibility
  • Air pressure
  • Humidity (amount of water vapour in the air)
  • Sunshine
A boy checks the weather readings of a Stephenson screen

Temperature is measured in Celsius (°C) using a thermometer. The thermometer must be shaded from direct sunlight and should have air circulating around it. The thermometers can be placed in a Stevenson Screen. This is a wooden box with slatted sides, a sloping roof and legs to keep the screen off the ground. It is painted white to reflect the sun.

Precipitation is measured using a rain gauge. This is a funnel inside a graduated container. The depth of the rain in millimetres can be read from the side of the container.

Man uses anemometer to measure the strength of the wind at sea

Wind direction is reported by the direction it is blowing from, according to the compass. Wind blowing from the west is travelling eastwards so is called a westerly wind, not an easterly wind.

Wind speed can be measured using an anemometer. The strength of the wind is measured on the Beaufort scale.

A house with chimney, tree and flag and no movement

Beaufort number 0

Calm with windspeeds of almost zero

Otka chart held up to the sky

Cloud cover is measured in units called oktas. Each okta represents one eighth of the sky covered by cloud.

Air pressure. Air is light but because there is so much of it above us, it exerts a pressure on us. Air pressure is measured by a barometer. The units used are millibars. The greater the reading, the higher the pressure.

A high-pressure system is called an anticyclone. Air falls in an anticyclone so no clouds are formed. In summer, high pressure usually results in clear skies, gentle breezes and fine weather. In winter high pressure leads to clear skies and colder conditions.

An area of low pressure is called a depression. Air rises in a depression so clouds and rainfall are formed. Depressions therefore bring unsettled weather and rain. Winds are normally stronger. They usually form over the Atlantic Ocean and are carried across Britain by westerly winds.