Weather and climate

Weather is what the air outside is like today: hot or cold, wet or dry, windy or calm, cloudy or clear. Climate is the usual weather of a place, worked out from many years of measurements. We measure the weather with instruments and record it to find patterns.

Key facts

  • Weather: the conditions on one day. Climate: the average weather of a place over many years (usually 30).
  • Instruments: thermometer – temperature (°C); rain gauge – rainfall (mm); wind vane – wind direction; anemometer – wind speed; barometer – air pressure.
  • A wind is named after the direction it blows from: a north wind blows from the north.
  • Clouds: cumulus are white and fluffy (fair weather); stratus are a flat grey layer (dull, drizzly); cirrus are high and wispy (made of ice); cumulonimbus are huge, tall storm clouds (thunder, lightning, heavy rain).
  • High air pressure usually brings settled, dry weather; low pressure brings cloud, wind and rain.
  • Climate zones: polar (very cold), temperate (mild, with four seasons), Mediterranean (hot, dry summers and mild, wet winters), desert (very dry) and tropical (hot and wet all year).

Worked examples

Example 1

Which instrument measures each of these: the temperature, the rainfall, the wind direction and the wind speed?

  1. Temperature, in °C: a thermometer.
  2. Rainfall, in mm: a rain gauge collects the rain.
  3. Wind direction: a wind vane points to where the wind comes from. Wind speed: an anemometer’s cups spin faster in a stronger wind.

Answer: thermometer; rain gauge; wind vane; anemometer

Example 2

The midday temperatures for a week were 14, 17, 12, 15, 19, 16 and 12 °C. Find the mean and the range.

  1. Add the seven temperatures. 14 + 17 + 12 + 15 + 19 + 16 + 12 = 105
  2. Divide by how many days. 105 ÷ 7 = 15°C
  3. Range = highest − lowest. 19 − 12 = 7°C

Answer: mean 15°C; range 7°C

Example 3

Is each sentence about weather or climate? “It is raining in Durban today.” “Cape Town has hot, dry summers and wet winters.”

  1. “Raining today” describes one day: weather.
  2. “Hot, dry summers and wet winters” is the usual pattern, year after year: climate (Cape Town has a Mediterranean climate).

Answer: the first is weather; the second is climate

Example 4

A cloud grows very tall, with a dark base and a flat, spreading top. What type of cloud is it, and what weather might it bring?

  1. Very tall, towering cloud with a flat top: cumulonimbus, the biggest cloud of all.
  2. Cumulonimbus clouds bring thunderstorms: thunder, lightning, heavy rain and sometimes hail.

Answer: cumulonimbus; thunderstorms with lightning, heavy rain and sometimes hail