What Is Air Temperature?
Air temperature describes how warm or cold the atmosphere is. At the molecular level, it reflects the average kinetic energy of the gases in the air: faster-moving molecules correspond to a higher temperature, while slower-moving molecules correspond to a lower one.
The number in a weather forecast is the temperature of the air itself, measured under standardized conditions. It does not include the extra warmth of direct sunlight, the cooling effect of wind on skin, or the influence of humidity on how efficiently sweat evaporates. Those effects belong to apparent or feels like temperature.
Temperature affects almost every other part of the weather. It influences whether precipitation falls as rain, sleet, or snow, how much water vapour the air can contain, how pressure systems develop, and how stable or unstable the atmosphere becomes.
How Air Temperature Is Measured
A thermometer left in direct sunlight does not give a reliable air temperature. Solar radiation heats the instrument itself, so its reading may rise far above the temperature of the surrounding air. Buildings, concrete, vehicles, and dark surfaces can distort a reading in the same way.
Official weather stations protect temperature sensors inside a ventilated instrument screen. A traditional Stevenson screen is a white, louvred enclosure that blocks direct sunlight and precipitation while allowing air to flow through. Modern stations may use smaller radiation shields with natural or fan-assisted ventilation.
The sensor is normally positioned about 1.25 to 2 metres (4 to 6.5 ft) above open ground, away from buildings and other sources of artificial heat. Many automatic stations use platinum resistance thermometers or thermistors, which can record and transmit observations continuously.
These standards make readings from different places comparable. A rooftop sensor, a thermometer above asphalt, and an official station outside a city can all report different values without any of them being broken. They are measuring different local environments.
Celsius, Fahrenheit, and Kelvin
Most forecasts use one of two everyday temperature scales:
- Celsius (°C) is used by most countries and in meteorology. Water freezes at 0°C and boils at about 100°C (32°F and 212°F) at standard sea-level pressure.
- Fahrenheit (°F) is used mainly in the United States and a few other places. Water freezes at 32°F and boils at about 212°F at standard sea-level pressure.
Scientists also use kelvin (K) for thermodynamic temperature. The size of one kelvin is the same as one degree Celsius, but the scale starts at absolute zero. A temperature of 0°C is equal to 273.15 K. Kelvin values do not use a degree symbol.
Quick Reference
Celsius Fahrenheit Typical conditions -20°C -4°F Very cold -10°C 14°F Cold, with ice likely 0°C 32°F Freezing point of water 10°C 50°F Cool 20°C 68°F Mild for many people 30°C 86°F Hot 40°C 104°F Extreme heatComfort depends on humidity, wind, sunshine, clothing, activity, and what your body is accustomed to. The descriptions in the table are useful reference points, not universal comfort categories.
Converting Between Celsius and Fahrenheit
- Celsius to Fahrenheit: multiply by 1.8, then add 32.
- Fahrenheit to Celsius: subtract 32, then divide by 1.8.
For a quick estimate, double the Celsius value and add 30. This shortcut is less accurate at very high or low temperatures, but it is useful around common outdoor values. For example, 20°C becomes roughly 70°F, compared with the exact value of 68°F.
Why Temperature Changes Through the Day
The Sun heats the ground, and the ground then warms the air above it. After sunrise, the surface usually receives more energy than it loses, so the temperature rises. Heating continues after solar noon, which is why the warmest part of a fair-weather day often arrives in the mid or late afternoon rather than when the Sun is highest.
After sunset, the ground loses heat by emitting infrared radiation. The air near the surface cools with it, and the minimum temperature often occurs around sunrise. These are common patterns, not fixed rules. A cold front can send temperatures falling in the middle of the day, while increasing cloud or wind can cause the overnight minimum to occur much earlier than sunrise.
The difference between the daily maximum and minimum is called the diurnal temperature range. Several conditions control its size:
- Cloud cover reflects sunlight during the day and slows heat loss at night, usually narrowing the range.
- Humidity also tends to limit the day-to-night swing because water vapour affects how heat is stored and released.
- Wind mixes warmer and cooler layers of air, reducing sharp changes near the ground.
- Dry, clear, calm weather often produces warm afternoons and cold nights, especially inland.
- Oceans and large lakes heat and cool slowly, so nearby areas usually have smaller temperature swings.
- Snow cover reflects much of the incoming sunlight and can keep daytime temperatures low.
The cloud cover resource explains in more detail why cloudy days have cooler highs and cloudy nights often have warmer lows.
What Maximum and Minimum Temperatures Mean
The maximum temperature is the highest air temperature recorded or forecast during a stated period. The minimum temperature is the lowest. On a daily forecast, these are usually presented as the day’s high and overnight low.
Always check which period the values cover. An overnight low may belong to the coming night, while another service may assign it to the calendar day on which it occurs. Around midnight, this can make two forecasts look different even when they predict the same temperature curve.
Hourly values provide the missing context. They show whether the day warms steadily, cools after a front, or reaches its minimum before dawn and then rises quickly. They also help with frost, travel, and outdoor planning when a single high and low are too broad.
Air Temperature and Feels Like Temperature
Air temperature describes the atmosphere under standardized conditions. Your body exchanges heat with the air, wind, surrounding surfaces, and sunlight, so the same measured temperature can feel very different from one day to the next.
In hot weather, high humidity slows the evaporation of sweat and makes it harder for the body to cool. Heat index calculations combine temperature and relative humidity to estimate this effect. In cold weather, moving air carries heat away from exposed skin more quickly. Wind chill combines temperature and wind speed to describe that added cooling.
Direct sunlight adds radiant heat, but many apparent-temperature formulas assume shade. Clothing, activity, age, health, and exposure time also affect personal comfort. This is why a feels like value is useful guidance rather than a replacement for the measured air temperature.
Why Your Thermometer May Disagree With the Forecast
A home thermometer and a nearby forecast can differ for several reasons:
- Sun exposure can warm the sensor above the true air temperature.
- Walls, balconies, roofs, and paving absorb and release heat, especially in built-up areas.
- Height above the ground matters because the surface can be much warmer by day and colder on clear nights.
- Distance and elevation matter if the forecast represents a weather station or model grid point several kilometres away.
- Sensor response time can make a device lag behind a rapid temperature change.
- Observation timing and rounding can create small differences even at the same location.
For a better home reading, place the sensor in a shaded, well-ventilated spot above natural ground and away from walls, windows, air-conditioning outlets, and paved surfaces. It still will not be an official observation site, but the reading will better represent the surrounding air.
Temperature, Altitude, and Inversions
In the lower atmosphere, temperature decreases with height by an average of about 6.5°C per 1,000 metres (3.6°F per 1,000 ft). This average, known as the environmental lapse rate, is useful for broad comparisons but should not be treated as a conversion rule for every mountain.
The actual rate changes with humidity, cloud, wind, time of day, and the movement of air. Rising dry air cools faster than saturated air because condensation releases heat. A valley and a nearby ridge can therefore have a much smaller or larger difference than the average suggests.
Sometimes temperature increases with height through a shallow layer. This is a temperature inversion. On clear, calm nights, cold dense air can drain into valleys while higher slopes remain milder. Inversions can also trap fog and air pollution near the surface, so the coldest place may be the valley floor rather than the highest ground.
How Temperature Is Forecast
Weather models calculate how heat moves through the atmosphere, ground, and water. They account for incoming sunlight, cloud, wind, humidity, soil moisture, snow cover, terrain, and the arrival of warmer or colder air. The standard near-surface forecast usually represents air temperature at roughly 2 metres (6.5 ft) above the ground.
Local details are difficult to represent perfectly. A model grid may contain hills, streets, woodland, and water within a single cell. Forecast systems adjust model output for elevation and known local patterns, but a sheltered valley, exposed coast, or dense city centre can still behave differently.
Temperature is generally easier to forecast than showers or fog, but errors in cloud cover, wind direction, or the timing of a weather front can shift the result by several degrees. The resource on how weather forecasts work explains why the forecast changes as new observations arrive.
How Airpult Shows Temperature
Airpult shows the current temperature alongside the feels like value, daily maximum and minimum, and hourly changes. Looking at these together gives a clearer picture than the daily high alone. You can also switch between Celsius and Fahrenheit in your settings.
Compare temperature with humidity, wind, cloud cover, and precipitation to understand why conditions may feel different from the number shown. Use the explore page to search for any location and check its temperature forecast.
