Key: orange dots = warm air, blue = cold air, teal = moist air. Blue triangles mark a cold front and red semicircles a warm front, as on a weather map. Heights, speeds and the station readings are simplified teaching values, not a real forecast; the vertical scale is stretched so you can see the air move.
Meteorologists draw isobars (lines of equal air pressure), H for high pressure, L for low pressure and fronts where warm and cold air meet. Pick a town, forecast its weather, then check. On a phone, swipe the map sideways.
Close isobars = strong wind. Air flows counterclockwise and inward around a low in the Northern Hemisphere (clockwise in the Southern), and clockwise and outward around a high. Fronts move in the direction their triangles and semicircles point.
A climate graph shows the average temperature (line) and precipitation (bars) for each month, worked out from about 30 years of weather records. Tap a city on the map. Compare two cities to see how latitude, the ocean and the monsoon change climate.
Data: monthly averages (daily mean temperature, total precipitation) from the national weather services, mostly 1991–2020, as listed in Wikipedia’s climate tables (London: Greenwich Park; Sydney: Observatory Hill); rounded. Köppen codes: A tropical, B dry, C temperate, D continental, E polar.
Tap a card, then tap the box it belongs in. Press Check when all 12 are placed. Tap the empty card area to put a selected card back.
Meteorologists measure the weather with these instruments. Pick Basic (7 labels) or Advanced (12). Switch between the labeled diagram, a blank one, a label quiz and match the jobs. On a phone, swipe the diagram sideways.
Tap a word, then tap the numbered box it belongs to (on the diagram or in the list below). Tap a filled box to take the word back.
Each line describes the job of one part. Tap a part name, then tap the box next to the job it does. Tap a filled box to take the word back.
A printable worksheet with an answer key: label the weather station, weather or climate, read the weather map and forecast for four towns, compare the climate data of Dhaka and London, fronts and pressure, and two explain questions. The label part uses the level chosen in the diagram above.
Weather is the state of the air at one place and time: temperature, air pressure, wind, humidity, clouds and precipitation (rain, snow, sleet, hail). It can change within hours. Climate is the typical weather of a place over many years: “Dhaka has a wet monsoon summer” is climate; “it is raining in Dhaka now” is weather.
The Sun heats the ground and sea unevenly. Land heats up and cools down faster than water, so on a sunny day air over the land warms, expands and rises, and cooler air flows in from the sea (a sea breeze). Rising air cools; when it cools enough, its water vapor condenses into the tiny droplets that make clouds. That is why clouds and rain go with rising air and low pressure, and clear skies with sinking air and high pressure. Wind blows from high to low pressure; the closer the isobars, the stronger the wind.
Large bodies of air take on the temperature and humidity of where they formed (air masses). Where two meet is a front. At a cold front, dense cold air wedges under warm air and lifts it steeply: towering cumulonimbus, heavy showers, a sharp drop in temperature and a wind shift. At a warm front, warm air rides gently up over cold air: cirrus first, then thickening layer cloud and hours of steady rain. Earth’s rotation (the Coriolis effect) turns winds so they circle around lows and highs instead of blowing straight in or out.
Latitude (how high the Sun gets), distance from the sea (oceans keep coasts milder), altitude (colder higher up), prevailing winds and mountains (rain on the windward side, rain shadow behind), ocean currents and seasonal winds such as the monsoon. Because of these, Cairo and Dhaka, both between about 24° and 30° N, have very different climates. Today human greenhouse-gas emissions are also changing climates: the global average temperature has risen by more than 1 °C since the late 1800s.
Play the Cold front and watch the station graph: pressure falls, then rises after the front; the temperature drops. Compare it with the Warm front. Then compare the climate graphs of London and Moscow (ocean versus inland), and Cairo and Dhaka (desert versus monsoon).
| Measures | Instrument | Unit | What it tells a forecaster |
|---|---|---|---|
| Air temperature | Thermometer (in a Stevenson screen) | °C or °F | Kept in the shade, about 1.25–2 m above grass, so it measures the air, not sunshine |
| Air pressure | Barometer | hPa (= millibars) | Falling pressure: a low or a front is coming; rising pressure: settling weather |
| Wind speed | Anemometer | km/h, m/s or knots | Strong winds come with tightly packed isobars |
| Wind direction | Wind vane | Compass direction | Named for where the wind comes from; a change often marks a front |
| Precipitation | Rain gauge | mm | 1 mm of rain = 1 liter of water on each square meter |
| Humidity | Hygrometer | % relative humidity | Near 100% the air is saturated: fog, cloud or dew |
| Upper air | Weather balloon + radiosonde | — | Temperature, humidity and wind up to about 30 km, launched twice a day worldwide |
| Clouds and storms | Weather satellite, weather radar | — | Satellites see cloud from space; radar shows where rain and hail are falling |
Puffy heaps of cloud made by rising air. Small cumulus mean fair weather; a cumulonimbus can tower 10 km or more and brings thunder, lightning, hail and heavy showers.
Flat gray layers when a wide sheet of air is lifted gently, as at a warm front. Nimbostratus gives long periods of steady rain or snow.
Thin, wispy ice-crystal clouds very high up. Spreading cirrus is often the first sign of an approaching warm front.
Weather is the state of the atmosphere at a particular place and time: temperature, air pressure, wind, humidity, clouds and precipitation, which can change within hours. Climate is the long-term pattern of weather in a place, usually the averages and extremes over 30 years. One rainy day is weather; a rainy season every year is climate.
Key takeaway: weather is today, climate is the long-term average.Wind is air moving from areas of high air pressure to areas of low pressure. Pressure differences come from uneven heating: warm air rises and leaves lower pressure at the surface, while cool, sinking air makes higher pressure. The bigger the difference over a distance, the stronger the wind. Earth’s rotation turns the wind so that it circles around highs and lows.
Key takeaway: air flows from high to low pressure.When air rises it expands and cools. At lower temperatures less water can stay as vapor, so at the dew point the vapor condenses onto tiny particles of dust, salt or smoke, forming cloud droplets. Inside the cloud, droplets collide and grow (or ice crystals grow and then melt) until they are heavy enough to fall as rain, snow or hail.
Key takeaway: rising air cools, vapor condenses, droplets grow and fall.A front is the boundary between two air masses of different temperature and humidity. At a cold front, cold air pushes under warm air and lifts it steeply, causing towering clouds, heavy showers and a drop in temperature. At a warm front, warm air glides up over cold air, causing wide layer clouds and long, steady rain. On weather maps, cold fronts are blue lines with triangles and warm fronts red lines with semicircles.
Key takeaway: cold fronts: short and heavy; warm fronts: long and steady.In a high-pressure area (anticyclone) air sinks and warms, so clouds rarely form: usually dry, settled weather with light winds, hot in summer and frosty or foggy in winter. In a low-pressure area (depression) air rises, cools and forms clouds, so lows bring cloud, wind and rain, often with fronts.
Key takeaway: high pressure: settled; low pressure: unsettled.On a sunny day the land heats up faster than the sea. Air over the land warms, rises and leaves slightly lower pressure, so cooler air from over the sea flows in toward the land: a sea breeze. At night the land cools faster than the sea and the flow reverses: a land breeze blows out to sea.
Key takeaway: land heats and cools faster than water.When moist wind meets a mountain range it is forced upward, cools and drops much of its water as rain or snow on the windward side. The air that sinks down the other side is dry and warms up, so the leeward side gets far less rain. Death Valley behind the Sierra Nevada and the Tibetan Plateau behind the Himalayas are examples.
Key takeaway: mountains wring the rain out of the air.Latitude (how much sunlight a place gets through the year), distance from the sea (oceans keep coasts milder), altitude (higher means colder), prevailing winds and mountains (rain on the windward side, rain shadow behind), ocean currents, and seasonal winds such as the monsoon. Human greenhouse-gas emissions are now warming climates worldwide.
Key takeaway: latitude, ocean, altitude, winds and mountains.A climate graph shows twelve months along the bottom. The bars show the average precipitation for each month (scale usually on the right, in mm) and the line shows the average temperature (scale on the left, in °C). Look for the warmest and coldest months, the temperature range, the total yearly precipitation and whether the rain falls all year or in one season.
Key takeaway: line for temperature, bars for precipitation.It shows the real processes (air rising over warm land, condensation, fronts lifting warm air, rain shadows and storm downdrafts) and the station readings change in the realistic direction, for example pressure falling before a cold front and rising after it. But it is a teaching model: the vertical scale is stretched, the numbers are typical rather than calculated, and real weather is far more varied. The climate graphs use real measured averages.
Key takeaway: real processes, simplified numbers; real climate data.