Weather vs climate

Weather is the day-to-day state of the atmosphere at a place — temperature, rain, wind, cloud. Climate is the average weather of a place taken over a long period (usually 30+ years). We record weather using standard instruments so measurements can be compared fairly.

• Temperature — measured with a digital thermometer in °C.
• Precipitation — a rain gauge measures rainfall in mm.
• Atmospheric pressure — a barometer reads pressure in millibars (mb).

Instruments & units

Each weather element has its own instrument and unit:

• Wind direction — a wind vane shows the direction the wind blows from, given as one of the 8 compass points.
• Wind speed — an anemometer (spinning cups) measures speed in knots.
• Cloud type — identified by shape/height: cirrus (high, wispy), stratus (low, layered), cumulus (fluffy), cumulonimbus (tall storm clouds).
• Cloud cover — estimated in oktas (eighths of the sky covered).

Forecast data comes from many sources: land-based weather stations and rainfall radar; geostationary and polar-orbiting satellites from the air; and buoys at sea.

Which instrument?

Match the element to its unit

Tap an element, then tap the unit it is measured in.

Four factors affecting climate

Why is the climate of one place different from another? Four main factors:

• Latitude — places near the Equator receive more concentrated, direct sunlight than places near the poles, so they are warmer.
• Prevailing winds — the direction winds usually blow from decides whether a place gets warm or cold, wet or dry air (the British Isles' prevailing wind is from the south-west).
• Distance from the sea — the sea heats and cools slowly, so coasts have mild winters and cool summers (maritime); inland areas have hot summers and cold winters (continental).
• Altitude — temperature falls by roughly 1°C for every 100 m of height gained, so highland areas are colder.

Your turn — altitude and temperature

Air masses over the British Isles

An air mass is a large body of air that takes on the temperature and moisture of the region where it forms. The British Isles sits where several meet, which is why our weather is so changeable. Air masses are named by temperature (tropical = warm / polar = cold) and source (maritime = over sea, moist / continental = over land, dry):

• Tropical maritime — warm and moist (from the south-west Atlantic); mild, cloudy, wet.
• Tropical continental — warm and dry (from North Africa/Europe in summer); hot, dry spells.
• Polar maritime — cold and moist (from the north-west Atlantic); cool, showery.
• Polar continental — cold and dry (from Eurasia in winter); very cold, dry, frosty.

Name that air mass

Frontal depression (low pressure)

A depression forms where warm tropical air meets cold polar air. The lighter warm air is forced to rise, so pressure falls and the weather is unsettled — cloudy, wet and windy. As a depression passes over, the weather changes in a set order:

Reading a depression

Anticyclone (high pressure)

An anticyclone is a large area of high pressure where air sinks. Sinking air stops clouds forming, so anticyclones bring calm, settled, dry weather that can last for days — but the season changes what that feels like:

• Summer anticyclone — hot, sunny days; clear nights; risk of heat and thunderstorms building.
• Winter anticyclone — cold, still days; clear skies let heat escape at night giving frost, fog and mist.

Contrast to remember: depression = low pressure, unsettled and wet; anticyclone = high pressure, settled and dry.

Match each pressure system to its weather

Tap a feature on the left, then its matching description on the right.

Reading synoptic charts

A synoptic chart is a weather map that summarises conditions using symbols:

• Isobars — lines joining places of equal pressure. Closely spaced isobars mean a steep pressure gradient and strong winds; widely spaced isobars mean light winds.
• Fronts — a warm front (red, round bumps), a cold front (blue, triangles) and an occluded front (purple) show where air masses meet.
• Pressure — a low centre is marked L, a high centre H, with values in millibars.

Satellite images add cloud cover, so forecasters combine both. Forecasting has limits: the atmosphere is chaotic, so accuracy falls the further ahead the forecast reaches.

Your turn — pressure difference

Impacts of extreme weather

Sometimes weather becomes extreme enough to cause disaster. CCEA requires a case study of one extreme weather event from OUTSIDE the British Isles — a tropical storm (hurricane), a tornado, or a drought. Impacts are usually grouped as:

• Social — deaths, injuries, homelessness, disease, disrupted schooling.
• Economic — damaged homes, roads and businesses; cost of rebuilding; lost harvests and jobs.
• Environmental — flooding, landslides, contaminated water, destroyed habitats.

Case study flag: your teacher will choose the specific event (for example a named hurricane, tornado outbreak or drought). Do not quote wind speeds, death tolls or costs from memory — check the exact figures against your class notes.

Your turn — reading rainfall data

Classifying impacts

The big ideas to know

You've covered all of CCEA Theme C — Our Changing Weather & Climate. Press Finish to see your score.