Weather: measuring and forecasting
The difference between weather and climate, the instruments that measure weather, why the wind blows from high to low pressure, weather fronts, and how forecasts are made. With a class weather station.
Read
Weather is the short-term state of the atmosphere, over hours or days. Climate is the average weather over a long time, usually 30 years.[1][2]
Weather stations measure temperature with a thermometer kept in a box called a Stevenson screen, rain with a rain gauge, wind speed with an anemometer and wind direction with a weather vane. Air pressure is measured with a barometer, and cloud cover is counted in eighths of the sky (oktas).[3]
A wind is named after the direction it comes from: a west wind blows from the west.[3]
Air presses on everything. At sea level the average air pressure is about 1013 hectopascals (hPa). High pressure often brings clear blue skies; low pressure generally brings wind and unsettled weather.[9][8]
Why the wind blows: the Sun heats the Earth unevenly. Warm air rises, leaving lower pressure, and cooler air sinks, making higher pressure. Air moves from high to low pressure, and the bigger the difference, the faster the wind.[7]
Clouds form when moist air cools until it cannot hold any more water vapour. The water condenses into tiny droplets around specks of dust, salt or smoke, and millions of them must join to make one raindrop.[6][5]
A weather front is the boundary where two different air masses meet, often bringing a change in the weather. On weather maps a cold front is a blue line with triangles and a warm front a red line with semicircles.[10]
Forecasts: millions of observations are collected every day from satellites, weather stations, ocean sensors and radar. Supercomputers use them to calculate how the atmosphere will change, and forecasters check and adjust the result.[11]
Try it: Run a class weather station
You need
- A home-made rain gauge (plastic bottle with funnel and ruler)
- A thermometer
- A ribbon or strip of plastic bag tied to a stick (wind streamer)
- A compass
- A weather record sheet
Safety
Stay in the school grounds with an adult. Never look at the Sun. Glass thermometers break easily: handle with care. The teacher cuts the bottle for the rain gauge and tapes the edge.
What to do
- Choose an open spot in the school grounds, away from walls and trees. Put the rain gauge there.
- Every day at the same time, read the temperature in the shade (not in sunshine).
- Hold up the wind streamer. Use the compass to find where the wind comes FROM, and note how strong it is (calm, light, strong).
- Look at the sky: how many eighths (oktas) are covered with cloud?
- Read the rain gauge in millimetres, then empty it.
- Compare your readings with the forecast from the day before. Was the forecast right?
Play: Which instrument?
Which instrument would a weather station use to measure this?
Your best score is kept only on this device. Nothing is sent anywhere.
Quiz
Other ages: Ages 6–7 · Ages 15–16