You wake up, pull back the curtains, and rain is hammering the window. By lunchtime the sun is out and your coat is too warm. That is weather — the ever-changing state of the air around you, hour by hour.
Weather versus climate
- Weather is the day-to-day condition of the atmosphere: today, this hour, right now.
- Climate is the average weather of a place worked out over about 30 years — its usual pattern.
A single snowy day in April is weather. The fact that British winters are usually cool and damp is climate. A good saying: climate is what you expect, weather is what you get.
| Feature | Weather | Climate |
|---|---|---|
| Time scale | Minutes to days | About 30 years |
| Changes | Very quickly | Slowly |
| Example | Rain this afternoon | Warm dry summers |
The elements of weather
- Temperature — how hot or cold the air is, measured with a thermometer in degrees Celsius.
- Rainfall (precipitation) — rain, sleet, hail or snow, collected in a rain gauge in millimetres.
- Wind — moving air; its speed is measured with an anemometer and its direction with a wind vane.
- Air pressure — the weight of the air, read on a barometer; low pressure often brings rain, high pressure brings calm dry spells.
- Humidity — how much water vapour the air holds.
- Cloud cover — how much of the sky is covered, judged in eighths called oktas.
Weather stations gather all six elements together, several times a day, so that patterns can be spotted and forecasts made. Over many years these daily readings are averaged to describe a place's climate.
Reading a climate graph
A climate graph shows a whole year on one picture. The bars show average rainfall each month (read the left-hand axis) and the line shows average temperature (read the right-hand axis). To read it: find the month, look up to the top of the bar for rainfall, and to the line for temperature.