Understanding the Weather

The elements of weather, the instruments and units used to measure them, temperature range and mean, air pressure and how forecasts help us.

Key ideas

• Weather is the state of the atmosphere at a given time and place; climate is the pattern of weather over decades.
• The five elements of weather are temperature, air pressure, wind, precipitation and humidity.
• Almost all weather happens in the troposphere, the lowest layer of the atmosphere.
• Wind blows from high pressure to low pressure; air pressure is lower on high places because less air presses down.
• Humidity is the water vapour in the air; at 100 per cent relative humidity the air is saturated.
• Rain, snow, sleet and hail are all forms of precipitation.
• Forecasts help farmers decide when to sow, water or harvest, and warn people before storms.

Remember

Watch out

• Mixing up weather (today) and climate (the long-term pattern).
• Mixing up a wind vane (direction) and an anemometer (speed).
• Saying wind blows from low to high pressure: it blows from high to low.

Worked example