Understanding the Weather | CBSE Class 7 Geography Notes

This note covers daily conditions of the air around us, their measurement, instruments and records, natural clues, predictions, temperature calculations, weather maps, and preparation for severe conditions.

What is weather, and which elements describe it?

Weather means the condition of the Earth's atmosphere at a particular place and time. The atmosphere is the surrounding layer of gases, which we call air on Earth. Describing weather therefore involves saying both where and when the conditions occur.

The troposphere is the atmospheric layer nearest the ground. All land-based plants and animals live and breathe within it. Almost all weather phenomena occur here. The word “almost” matters: it does not mean that every weather phenomenon occurs in this layer.

The troposphere reaches a height of 6 to 18 kilometres. It is thinner at the poles, where cold air contracts, and thicker in the tropical zone, where warmer air expands. The poles are Earth's northern and southern ends; the tropical zone is the region around the equator, the imaginary line halfway between the poles.

What are the five elements?

Elements of weather are the conditions considered together when describing the weather. Feeling hot, noticing rainfall, or seeing trees move in the wind tells us about different elements. No single one gives the complete description.

Water vapour is water in its gaseous form. Sleet means rain that is frozen or partly frozen. Hail consists of small, hard ice balls falling from the sky. These terms distinguish water present in the air from water falling to the ground.

Different elements can dominate in different situations: rainfall in July, temperature in May and December, or wind during a loo, the strong, hot and dusty summer winds of north India. An element becoming especially noticeable does not remove the other elements from the weather.

Why do we need measurements as well as natural clues?

Words such as cold, pleasant and chilly describe an experience, but people may experience the same weather differently. Krishnan in Chennai might feel chilly after rain, while Amir in Kashmir might find the same conditions pleasant. A shared measurement makes their comparison clearer.

A common standard is an agreed way of measuring something. Temperature readings allow people in different places to communicate about heat and cold without relying entirely on personal sensations. The same need applies to the other elements of weather.

What can observations of nature tell us?

To forecast is to predict conditions in advance. People have long used natural clues in forecasting: low-flying birds, ants carrying eggs, squirrels collecting nuts, loud frog calls, and pine cones opening or closing. Knowledge of such observations has passed between generations.

Traditional weather prediction continues in many parts of India, especially for the arrival of the monsoon, the seasonal wind system associated with the rains discussed here. Observing nature is therefore part of the history of understanding weather, alongside the development of precise measuring instruments.

The photographs show ants carrying eggs to higher ground, a green frog croaking in a forest of the Western Ghats in expectation of rain, and two pine cones with different degrees of opening. They illustrate observations used in discussing expected weather changes.

Reference: NCERT Class 7 Figures 2.3.1 to 2.3.3

Ants moving their eggs higher indicate an expected weather change, especially heavy rain. Pine cones respond to humidity: they close in humid conditions to protect seeds and open in dry conditions to release them. These are particular observations, not a numerical measurement of rainfall.

How does meteorology use instruments?

Meteorology is the systematic study of weather and how it changes. Its specialists, meteorologists, use measurements to try to predict conditions hours, days or even weeks ahead. Scientific monitoring supplies precise information that a description such as “it feels cold” cannot provide.

How do thermometers measure and record temperature?

A thermometer measures temperature. Temperature scales provide a shared numerical description: °C means degrees Celsius, while °F means degrees Fahrenheit. A reading of 15°C corresponds to 59°F. The number must be read with its scale.

Some thermometers show the ambient temperature, meaning the temperature of the immediate surroundings. Others record the day's maximum, its highest temperature, and minimum, its lowest temperature. These readings answer different questions about conditions during a day.

Thermometers often contain coloured liquid that expands as temperature rises. Digital thermometers are increasingly preferred because they are more precise and can store more data. “Often” does not mean that every thermometer contains coloured liquid.

What do temperature records help us calculate?

Statistics involves gathering and analysing data to identify patterns, understand events or make predictions. Temperature records support two useful calculations. The temperature range is the maximum minus the minimum over a stated period, usually 24 hours.

The mean daily temperature is obtained by adding the day's maximum and minimum, then dividing their sum by two. A range measures the difference between the extremes; a mean supplies a single value calculated from them.

Definition: Temperature range = maximum temperature − minimum temperature. Mean daily temperature = (maximum temperature + minimum temperature) ÷ 2. Here = means “equals”, − means subtraction, + means addition, and ÷ means division; brackets group the addition to be completed first.

Temperature also affects familiar processes. Snow melts quickly in warm conditions, coconut oil becomes solid in winter, and curd takes longer to set in cold weather. Such observations show temperature's effects, while a thermometer gives a measurement that people can compare.

How can we interpret a week's temperature data?

Case study: A city in Madhya Pradesh

The following record gives daily maximum and minimum temperatures for a city in Madhya Pradesh. Both columns use degrees Celsius. Each row belongs to its printed date, so the two values on a row must stay together when calculating that day's mean or range.

The highest maximum is 32°C on 03.03.2025. The lowest minimum is 14°C on 05.03.2025. Using these extremes gives a range of 32 − 14 = 18°C for the whole period shown. They come from different days because the question concerns the whole period.

How does a daily calculation differ?

For 03.03.2025, use the maximum of 32°C and minimum of 18°C from that row. The daily range is 32 − 18 = 14°C. The mean daily temperature is (32 + 18) ÷ 2 = 25°C.

1. Identify the period requested: a particular day or the complete record.
2. Select the maximum and minimum that belong to that period.
3. For the range, subtract the minimum from the maximum.
4. For a daily mean, add that day's maximum and minimum, then divide by two.
5. Give the result with degrees Celsius and the relevant date or period.

The maximum column rises from 29°C on 28.02.2025 to 32°C on 03.03.2025. It then falls to 30°C and 28°C before reaching 29°C on the final date. Describe that sequence rather than claiming that temperature rose throughout the week.

Note: A range and a mean answer different questions. The range of 18°C for the whole record is neither the daily range nor the mean daily temperature for 03.03.2025.

Every numerical conclusion above can be checked against the displayed readings. Keeping the original table separate from calculations also makes it possible to see which values are observations and which results have been worked out from them.

How does a rain gauge measure precipitation?

A rain gauge collects rainfall so that its depth can be measured. Rain enters a funnel and passes into a cylinder. A scale beside the collecting tube allows the water level to be read. Rainfall is expressed in millimetres, abbreviated as mm.

For example, a collected depth of 5 mm is reported as 5 mm of rainfall. A report of 30 mm of rainfall in a day gives both an amount and a period. When comparing rainfall records, keep these two parts of the information together.

A funnel sits above a narrow measuring tube inside a larger cylinder. The labels identify the collecting funnel, measuring tube and measuring scale. Numbered marks appear beside the tube.

See Fig. 2.6 in your NCERT textbook

How should rainfall be recorded?

A useful recording activity depends on the position of the gauge as well as reading the scale. Nearby objects must not block rain from reaching the instrument. The gauge also needs a flat, secure position so that wind will not tilt or overturn it.

1. Choose an open site away from objects that could obstruct rainfall.
2. Place the gauge on a flat surface where it will remain upright.
3. Read the collected water using the measuring scale.
4. Record the reading at the same time each day for a month.
5. If snow has collected, let it melt before measuring the water.

The record can then be used to calculate weekly averages and discuss differences between weeks. A weekly average summarises the daily rainfall readings for that week. It is calculated by adding the readings and dividing by the number of days recorded.

Precipitation includes more than rain, but the instrument reading discussed here is a depth of collected water. Letting snow melt before measurement connects frozen precipitation to that water measurement. It does not require treating unmelted snow depth as the same quantity.

How does atmospheric pressure change with height and weather?

Atmospheric pressure comes from the weight of the air above and around us. It is higher near the sea coast and lower at greater heights in mountains. Air becomes thinner as we climb, leaving less oxygen available for the lungs to take in.

With less oxygen entering the blood, the body works harder during movement. People sometimes feel tired, dizzy or breathless at high altitudes, meaning heights above sea level. “Sometimes” is essential: these effects are not described as an identical experience for every person.

Does low ground always have high pressure?

Pressure is not always high in plains or coastal areas. It can drop dramatically, producing a depression, also called a low-pressure system. Such a system can sometimes develop into a storm or even a cyclone, a severe storm system.

A barometer measures atmospheric pressure. Its readings are generally displayed in millibars, abbreviated as mb, a unit of pressure. Normal pressure at the sea coast is around 1013 mb. A reading below 1000 mb indicates a depression.

Note: Keep “around” with 1013 mb and “can sometimes” with the development of a storm or cyclone. Neither the usual coastal value nor the development of every low-pressure system is an unconditional rule.

Why do high-altitude travellers need time to adjust?

To acclimatise means to adjust to a new climate or condition. People travelling to high places are advised to pause on the way to allow this adjustment. This connects the measurement of pressure with its effects on the body.

At Khardung la in Ladakh, over 5600 metres above sea level, atmospheric pressure is generally about 650 millibars. Army personnel serve in such high-altitude conditions. Both “over” for the height and “generally about” for the pressure belong with these figures.

Two distinct ideas therefore need to be kept together: pressure changes with height, and pressure at a place can also change with weather. A coastal location does not prevent a low-pressure system from developing there.

How are wind direction and speed measured?

Wind moves from areas of high pressure towards areas of low pressure. To describe it, record both its direction and its speed. These details support forecasting and matter to people whose activities are affected by moving air.

A wind vane, or weather vane, has an arm that turns, with a pointer at one end and a tail at the other. Wind pushes the tail and turns the pointer in the wind's direction. It responds even to a light breeze.

What do a wind sock and an anemometer show?

A wind sock is a wind-direction indicator used on an airfield. It helps pilots judge wind direction during take-off and landing. Similar indicators are used in industries that release gases or ash.

An anemometer is a wind-measuring instrument. In the cup instrument, three or four metal cups turn around a vertical shaft. Stronger wind causes faster rotation. A meter counts the rotations during a set period and calculates wind speed.

The speed is expressed in kilometres per hour, written as km/h. The cup movement described here explains the speed measurement. Direction and speed remain separate pieces of information when describing the wind.

The left photograph shows a red-and-white wind sock on a pole beside an airfield. The right photograph shows an anemometer with three cups attached around an upright support.

See Fig. 2.10 in your NCERT textbook

Who needs wind information?

Air pilots and sailors need wind data because moving air strongly affects flying and sailing. Farmers also use wind direction to anticipate where rain might come from. Greater wind speed causes soil to dry faster, making speed relevant to farming as well.

Wind direction therefore helps answer where air is moving, while speed describes how fast it moves. A useful wind record preserves both details, rather than replacing them with a general word such as “windy”.

What does relative humidity tell us?

Humidity describes water vapour in the air. Its level depends on factors including temperature, wind, pressure and location. Comparisons between places need measurements: guessing that a coastal place is more humid does not supply a measured value for either place.

Relative humidity expresses humidity on a percentage scale. The symbol % means per cent, or “out of one hundred”. Air with no water vapour would have 0% relative humidity, but such air is impossible in natural conditions.

Air that is saturated, meaning full of water vapour under the conditions being considered, has 100% relative humidity. In practice, dry weather has relative humidity between 20% and 40%. Humid weather usually has values between 60% and 80%.

How does humidity affect drying?

Evaporation is the change of liquid water into water vapour. It causes cooling. When the air already contains much water vapour, water evaporates slowly. This is typically the situation on a rainy day.

Consider Delhi at 52% relative humidity and Kochi at 84%, with the same temperature in both places. Wet clothes are likely to dry faster in Delhi because the air is less humid. In Kochi, higher humidity slows evaporation under that comparison.

Note: The 60% to 80% range for humid weather is described as usual. It is not a maximum possible value: the comparison involving Kochi uses 84%, while saturation corresponds to 100%.

How is humidity measured and used?

A hygrometer measures humidity. Different types work on different principles. Humidity measurements are important in industrial activities such as food processing. Museums also monitor humidity because a dry environment helps them preserve their exhibits.

Humidity and precipitation should be distinguished. Humidity concerns gaseous water already in the air; precipitation concerns water falling from the sky. They are both weather elements, but they describe different conditions and are measured using different instruments.

How do weather stations bring measurements together?

A weather station brings weather instruments together at one location. Several instruments are needed because the weather includes several elements. Readings taken at regular intervals help people follow changing conditions and provide information for maps and forecasts.

A sensor is a device that detects a condition for measurement. An Automated Weather Station, abbreviated as AWS, uses sensors to measure and record weather data automatically. It is a self-operating system that supplies information without needing human intervention.

Which observations can an AWS record?

Automated stations are widely used in agriculture, aviation, meaning flying, and navigation, meaning directing a journey or route. They also support environmental monitoring, the observation of environmental conditions. Accurate information arriving in time helps these activities use weather measurements.

What is the Sikkim example?

In 2023, the National Disaster Management Authority installed an AWS at a glacial lake, a lake associated with a glacier, which is a mass of ice moving slowly over land, in Sikkim. Its altitude is more than 4800 metres above sea level. It provides early information about approaching weather conditions.

Both photographs show instruments on upright supports with solar panels. The lower photograph shows the Sikkim installation on rocky ground, with mountains behind it.

See Figs. 2.11 and 2.12 in your NCERT textbook

The value of a station lies in bringing repeated observations together. A single reading describes one measurement at one time; a continuing record allows changing conditions to be followed. Automated recording supports this collection of timely weather information.

How do forecasts and warning maps help people prepare?

Meteorologists collect instrument readings over long periods, analyse the data and apply scientific methods to try to predict weather. A weather forecast is therefore a prediction based on information, rather than a claim that all future conditions are already certain.

Climate change, the longer-term change in climate or usual weather conditions, makes extreme events such as droughts, floods and cyclones more frequent. A drought involves a prolonged shortage of rain; a flood involves water covering normally dry land. Accurate predictions help people prepare.

Local governments can gather resources and plan for disasters. Fishermen can be warned when stormy seas are expected. A coastal area might need to be evacuated, meaning people are moved away from danger, if a cyclone is expected.

How should a weather-warning map be read?

The India Meteorological Department, or IMD, was established in 1875. Its motto means “From the sun arises rain.” A weather-warning map issued by the department for 19 May 2024 combines colours with symbols to communicate different kinds of information.

The map uses coloured subdivisions and weather symbols. Its legend gives green as “No Warning”, yellow as “Watch (Be Updated)”, orange as “Alert (Be Prepared)” and red as “Warning (Take Action)”.

See Fig. 2.13 in your NCERT textbook

A map legend explains its colours and symbols. Here the colours indicate warning levels. Weather symbols identify conditions, including heavy rain, thunder and lightning, and heat waves, periods of unusually hot weather. The date tells the reader which day's warning is being shown.

Read the colour and symbol together: a colour tells you the level of warning, while a symbol identifies the weather involved. The map is a dated warning, so it should not be read as a permanent description of a region's conditions.

Use the weather-warning map for 19 May 2024 to match the icons to weather conditions. Identify the states with warning signs and the parts of India likely to be free from severe weather.

Which states are likely to face heat wave conditions? Examine Tripura and Lakshadweep, and use the symbols to identify the causes of the warnings in each place.

See Fig. 2.13 in your NCERT textbook

Why must the strength of a prediction be preserved?

Meteorologists try to predict conditions, and an expected cyclone might require evacuation. These expressions keep the distinction between a forecast and a confirmed event. Warnings help people act on expected conditions without pretending that every possible danger has already occurred.

How can a weather table be turned into a clear report?

Case study: Jammu and Kashmir on 01-02-2024

The evening record below contains temperature, rainfall, snowfall and humidity readings for Jammu and Kashmir. A clear report identifies the date, the station and the measurement before comparing places. The actual temperature is the temperature recorded, rather than a usual reference value.

In the headings, R/F means rainfall, and hrs means hours. The time 0830 means 8:30 in the morning; 1730 means 5:30 in the afternoon. The table distinguishes precipitation from 0830 to 1730 from the 24-hour period ending at 0830 on the given date.

The weather record uses ACT for actual, NOR for normal, and DEP for departure from normal, meaning the difference from the normal reference value. S/N means snowfall, cm means centimetres, and TR means a trace amount.

A minus sign before a temperature indicates a value below zero on the Celsius scale. A dash marks a missing reading, not a zero measurement. The recorded trace of rainfall at Srinagar is also kept distinct from a printed zero.

What comparisons does the record support?

Gulmarg has the lowest actual maximum, −2.6°C, and the lowest actual minimum, −7.6°C, among the listed stations. Muzafarabad has the highest actual maximum, 8.5°C, and highest actual minimum, 5.6°C. These are comparisons of the actual readings.

For the 24-hour rainfall column, Qazigund records 36.2 mm, while Srinagar records 13.4 mm. Gulmarg's humidity changes from 76% at 0830 to 100% at 1730. Srinagar records 89% at both times, so that row shows no change between those readings.

Do not treat rainfall for 0830 to 1730 as the same period as rainfall for the 24 hours ending at 0830. Likewise, humidity at one time is not a daily average. Clear reporting keeps units, dates, periods and missing entries attached to the values they describe.

Glossary

• Weather — The condition of the Earth's atmosphere at a particular place and time.
• Atmosphere — The layer of gases around Earth, collectively known to us as air.
• Troposphere — The atmospheric layer nearest Earth's surface, where almost all weather phenomena occur.
• Precipitation — Water falling from the sky as rain, snow, sleet or hail.
• Humidity — The amount of water vapour present in the surrounding air.
• Relative humidity — Humidity expressed on a percentage scale, with saturation corresponding to 100%.
• Meteorology — The systematic study of weather and its changes, supporting weather forecasting.
• Ambient temperature — The temperature of the immediate surroundings where the measurement is made.
• Temperature range — The maximum temperature minus the minimum during a stated period, usually 24 hours.
• Mean daily temperature — The sum of the day's maximum and minimum temperatures divided by two.
• Rain gauge — An instrument that collects rainfall so its depth can be measured.
• Barometer — An instrument for measuring atmospheric pressure, generally displaying readings in millibars.
• Anemometer — A wind-measuring instrument whose rotating cups allow wind speed to be calculated.
• Hygrometer — An instrument used to measure humidity, with different types using different principles.
• Automated Weather Station — A self-operating system using sensors to measure and record several weather elements.

Common errors and misconceptions

• Misconception: Weather means temperature alone. Correct: Temperature, precipitation, pressure, wind and humidity together describe conditions at a place and time.
• Misconception: Every weather phenomenon occurs in the troposphere. Correct: Almost all weather phenomena occur there; retain that qualification.
• Misconception: Temperature range is calculated by adding the maximum and minimum. Correct: Subtract the minimum from the maximum. Adding them and dividing by two gives the mean daily temperature.
• Misconception: Any sheltered position is suitable for a rain gauge. Correct: It needs an open site without rain-obstructing objects and a flat surface where it remains upright.
• Misconception: Pressure at the coast is always high, and every depression becomes a cyclone. Correct: Coastal pressure sometimes drops dramatically; a depression can sometimes develop into a storm or cyclone.
• Misconception: Relative humidity cannot exceed 80%. Correct: Humid weather usually falls between 60% and 80%, but saturated air has 100% relative humidity.
• Misconception: A dash in a weather table means zero. Correct: A missing value must remain missing. It cannot be converted into a zero measurement.
• Misconception: A warning-map colour identifies the weather event by itself. Correct: Colours show warning levels; symbols identify the conditions involved.

Exam-style questions with model answers

Q1. Define weather and name the atmospheric layer where almost all weather phenomena occur. [2 marks]

1. Weather is the condition of the Earth's atmosphere at a particular place and time.
2. Almost all weather phenomena occur in the troposphere, the layer closest to the Earth's surface.

Q2. On 03.03.2025, a city's maximum temperature was 32°C and its minimum was 18°C, where °C means degrees Celsius. Calculate the temperature range and mean daily temperature, showing the method for each. [4 marks]

1. The temperature range is found by subtracting the day's minimum from its maximum. Both readings must belong to the day in question.
2. Using the supplied readings, the range is 32 − 18 = 14°C. This expresses the difference between that day's extremes.
3. Mean daily temperature is found by adding the day's maximum and minimum, then dividing the sum by two.
4. The mean daily temperature is (32 + 18) ÷ 2 = 25°C. Complete the addition before the division.

Q3. Explain how to position a rain gauge and use it to keep a month-long daily record, including what to do if snow collects. Give five points. [5 marks]

1. Select an open location away from objects that could obstruct the rain. Water must be able to enter the collecting funnel without such obstruction.
2. Put the instrument on a flat surface and ensure that it is secure. It should not tilt or topple when wind blows.
3. Use the measuring scale to read the depth of the water collected in the cylinder. This gives the amount of rainfall collected.
4. Take and record the reading at the same time every day for a month. Keep the measurements as a daily record for comparison.
5. If snow has collected, allow it to melt before taking the measurement. Read the resulting water using the instrument's scale.

Q4. Explain why people sometimes feel breathless at high altitudes, what acclimatising means, and why travellers are advised to pause during ascent. [3 marks]

1. At higher altitudes, the air becomes thinner and atmospheric pressure is lower. Less oxygen is available for the lungs, and less reaches the blood.
2. The body consequently works harder during movement, so people sometimes feel breathless, dizzy or tired. Acclimatising means adjusting to a new climate or condition.
3. Travellers are advised to pause while going to high-altitude places so that their bodies have time to adjust to the new conditions.

Q5. Delhi has 52% relative humidity and Kochi has 84%, with equal temperatures; % means per cent. Wet clothes are placed in both locations. Where are they likely to dry faster, and why? [2 marks]

1. The clothes are likely to dry faster in Delhi, which has the lower relative humidity in the supplied comparison.
2. Water evaporates more slowly when air already contains much water vapour. Kochi's higher humidity therefore slows drying under these conditions.

Q6. Describe an Automated Weather Station, explain its use in recording weather, identify fields where it is used, and explain how forecasts can help people prepare for dangerous weather. Give five points. [5 marks]

1. An Automated Weather Station is a self-operating system that uses sensors to measure and record weather data, supplying information without needing human intervention.
2. Its observations include temperature, humidity, wind speed and direction, precipitation and atmospheric pressure. Bringing these measurements together supports monitoring of conditions.
3. Automated stations are widely used in agriculture, aviation, navigation and environmental monitoring. These fields benefit from accurate weather information supplied in time.
4. Meteorologists analyse measurements collected over long periods and use scientific methods to try to predict weather. Forecasts help local governments organise resources for possible disasters.
5. Fishermen can be warned about expected stormy seas. If a cyclone is expected, a coastal area might have to be evacuated to prepare for danger.

Q7. The IMD warning-map legend gives green as “No Warning”, yellow as “Watch (Be Updated)”, orange as “Alert (Be Prepared)” and red as “Warning (Take Action)”. Explain the four colours in order. [4 marks]

1. Green indicates that the map assigns no warning to that subdivision. Read it using the legend supplied with the dated map.
2. Yellow indicates a watch. Its instruction is to remain updated about the weather information for the area concerned.
3. Orange indicates an alert. Its instruction is to be prepared for the conditions about which the warning is issued.
4. Red indicates a warning. Its instruction is to take action in response to the weather danger identified on the map.

Q8. For 01-02-2024, actual maximum and minimum temperatures were: Srinagar 6.5°C and 0.2°C; Gulmarg −2.6°C and −7.6°C; Muzafarabad 8.5°C and 5.6°C. Rainfall over 24 hours ending at 0830 was Qazigund 36.2 mm and Srinagar 13.4 mm. Gulmarg's relative humidity was 76% at 0830 and 100% at 1730. Here °C means degrees Celsius, mm means millimetres, % means per cent, 0830 means 8:30 a.m., and 1730 means 5:30 p.m. Report the lowest maximum, lowest minimum, highest maximum, wetter station and Gulmarg's humidity change, using only these comparisons. [5 marks]

1. Gulmarg has the lowest actual maximum among the three temperature stations supplied. Its maximum is −2.6°C, below Srinagar's 6.5°C and Muzafarabad's 8.5°C.
2. Gulmarg also has the lowest actual minimum among those three stations. Its minimum is −7.6°C, compared with 0.2°C in Srinagar and 5.6°C in Muzafarabad.
3. Muzafarabad has the highest actual maximum in the supplied comparison, at 8.5°C. This statement compares maximum temperatures, rather than mixing maximum and minimum readings.
4. Qazigund is wetter in the supplied 24-hour rainfall comparison: it records 36.2 mm, while Srinagar records 13.4 mm for the same period.
5. Gulmarg's relative humidity rises from 76% at 0830 to 100% at 1730. These are readings at two stated times, not a daily average.

Key takeaways

• Weather describes atmospheric conditions at a particular place and time; almost all weather phenomena occur in the troposphere.
• Temperature, precipitation, atmospheric pressure, wind and humidity together describe weather, although one element may dominate a particular situation.
• Subtract minimum temperature from maximum to find the range; add them and divide by two for mean daily temperature.
• A rain gauge needs an open, stable position, with readings taken at the same time each day.
• Pressure decreases with increasing altitude, but pressure in coastal areas can also drop dramatically during changing weather.
• Wind direction and speed affect flying, sailing and farming; stronger wind makes the anemometer's cups rotate faster.
• High humidity slows evaporation; hygrometers measure humidity, while rain gauges measure collected rainfall depth.
• Weather stations gather repeated measurements, and forecasts help people and governments prepare for potentially dangerous conditions.

Test yourself

Why might “chilly” fail to communicate an exact temperature?

People may experience the same conditions differently. A shared temperature reading gives a more precise comparison than a personal sensation.

What does ambient temperature mean?

It is the temperature of the immediate surroundings where the measurement is being made.

What do pine cones do in humid and dry conditions?

They close in humid conditions to protect their seeds and open in dry conditions to release them.

Which instrument measures atmospheric pressure, and which unit does it generally display?

A barometer measures atmospheric pressure, generally displaying its readings in millibars, abbreviated as mb.

Why is the word “sometimes” needed when describing a depression becoming a cyclone?

A low-pressure system can sometimes develop into a storm or cyclone; that development is not described as inevitable.

What does 100% relative humidity represent?

It represents air saturated with water vapour, rather than a measured depth of rainfall.

Why does a weather station take repeated readings?

Readings at regular intervals help track changing conditions and provide information for weather mapping and forecasting.

How do colours and symbols perform different roles on a warning map?

Colours communicate warning levels, while symbols identify weather conditions. Both should be interpreted using the map's legend and date.