Understanding the weather is essential for everything from aviation safety to daily forecasts.
Understanding the weather is essential for everything from aviation safety to daily forecasts. At the Met Office, we use a blend of cutting-edge technology and time-tested methods to observe and record the atmosphere’s most important elements.
Here’s how we measure sunshine, cloud, visibility, atmospheric pressure, and radiation, ensuring our data is accurate, reliable, and useful for everyone.
Measuring rainfall
The Met Office measures rainfall using a network of rain gauges strategically placed across the UK. The standard instrument is the cylindrical rain gauge, which collects precipitation in a funnel and stores it in a measuring container. Observers or automated systems regularly record the depth of water collected, typically in millimetres, to determine the amount of rainfall over a set period. These gauges are carefully sited in open areas away from obstructions to ensure accurate readings.
In addition to traditional gauges, the Met Office increasingly uses automated tipping-bucket rain gauges, which record each time a small bucket fills and tips, providing real-time data for rainfall rate. This combination of manual and automated observations ensures a comprehensive and reliable record of rainfall, supporting everything from daily forecasts to long-term climate monitoring.
READ MORE: How we measure rainfall
Measuring temperature
Temperature measurement at the Met Office is fundamental to accurate weather forecasts and climate records. Air temperature is measured using platinum resistance thermometers (PRTs), which are highly sensitive and reliable. These thermometers are housed within Stevenson screens, white, louvered enclosures that shield the instruments from direct sunlight and precipitation while allowing air to circulate freely.
The PRTs are positioned 1.25 metres above the ground, and each screen typically contains two PRTs (one operational, one backup) along with liquid-in-glass thermometers for manual checks. The PRTs work by measuring the electrical resistance of a platinum wire, which changes predictably with temperature. Ground, soil and concrete temperatures are also recorded at many of our stations.
READ MORE: How we measure temperature
Measuring wind
Wind is measured using anemometers and wind vanes installed at weather stations across the country. The most common instrument is the cup anemometer, which measures wind speed by counting the rotations of cups spun by the wind. Wind vanes indicate wind direction. These instruments are mounted at a standard height, usually 10 metres above ground level, to ensure consistency. At some locations, ultrasonic anemometers are used, which measure wind speed and direction by detecting changes in the speed of sound between sensors.
READ MORE: How we measure wind
Measuring visibility
Visibility is a crucial parameter for meteorology and aviation. Traditionally, visibility was estimated by human observers, who would judge how well distant objects could be identified against the sky. Observers followed strict rules: the object must be identifiable, the estimate should be made at ground level with an uninterrupted horizon, and the lowest visibility value from any direction should be reported. For aviation, the prevailing visibility is always noted.
Today, most Met Office observing stations use automated sensors to measure visibility. These sensors determine the meteorological optical range, the distance over which a beam of light is reduced to 5% of its original intensity. The most common sensor uses forward scattering of light: a high-intensity xenon strobe generates a beam, and the sensor measures how much light is scattered by particles in the air. This method closely simulates human perception and provides accurate readings from a few metres up to tens of kilometres.
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Measuring atmospheric pressure
Atmospheric pressure is measured using barometers equipped with silicon capacitive pressure sensors, chosen for their repeatability and long-term stability. Accurate pressure readings are vital for meteorology and especially for aircraft safety during landing. To minimise errors, each instrument contains three separate sensors, and internal software checks for discrepancies between them.
Deploying pressure sensors requires care. Air movement across the sensor’s vent can cause pressure drops. Even indoor airflows or air conditioning can affect readings. To avoid these errors, sensors are exposed via a static pressure head, which minimises wind effects.
Pressure varies with height, dropping by about 1 hPa for every 10 metres of elevation. To compare readings from stations at different altitudes, all station-level pressures are converted to mean sea level pressure using a formula that accounts for air temperature. Every hour, synoptic stations report mean sea level pressure, station pressure, and pressure tendency (steady, rising, falling, etc.).
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Measuring cloud
Cloud type
Clouds are classified using World Meteorological Organisation criteria, based on their level (high, medium, or low) and genus (form and features). Common types include cumulus, stratocumulus, and stratus at low levels; altocumulus and nimbostratus at medium levels; and cirrus and cirrostratus at high levels. Cloud type reporting generally requires a human observer.
Cloud amount
Cloud amount is reported as the fraction of the sky covered by clouds, using oktas (eighths). Total cloud amount refers to all clouds, while partial cloud amount refers to each type or layer as if it were the only one present. Reporting conventions range from 0 oktas (clear sky) to 8 oktas (full cloud cover), with 9 oktas indicating sky obscured by fog or other phenomena.
Laser cloud base recorders estimate partial cloud amount by averaging the cloud detected directly above the instrument. Total cloud amount is only reported from stations with human observers.
Cloud base height
Cloud base is measured using pulsed diode laser LIDAR technology. Short, eye-safe laser pulses are sent vertically, and the backscatter from cloud surfaces is analysed to determine height. Modern recorders can detect up to three cloud layers simultaneously.
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Measuring sunshine and radiation
Sunshine
Sunshine duration was traditionally measured with the Campbell-Stokes sunshine recorder, a glass sphere that focuses sunlight onto a graduated card, burning a trace that corresponds to sunshine duration.
Modern sunshine sensors use arrays of photodiodes to estimate direct radiation intensity. A threshold of 120 Wm⁻² defines full sunshine. These sensors provide more accurate, automated readings.
Radiation
At some stations, four components of atmospheric radiation are measured:
- Global radiation: total downwelling short-wave radiation (visible to 4 µm), measured on a horizontal surface.
- Diffuse radiation: global radiation minus the direct solar component.
- Direct radiation: sunlight measured at normal incidence.
- Long-wave radiation: downwelling infrared wavelengths above 4 µm.
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Global radiation is measured by a pyranometer, which uses a thermopile to generate a voltage proportional to radiation intensity. Diffuse radiation measurements require a tracking device to obscure the sun. All instruments are calibrated against absolute cavity radiometers, ensuring traceability to world standards.
Keep up to date with weather warnings, and you can find the latest forecast on our website, on YouTube, by following us on X and Facebook, as well as on our mobile app which is available for iPhone from the App store and for Android from the Google Play store.