Outside air temperature is measured using electronic sensors housed inside ventilated, radiation-shielded enclosures, positioned about 1.5 to 2 meters above a flat grassy surface. This setup prevents sunlight, rain, and ground heat from skewing the reading, giving you the actual temperature of the air itself. The process is more carefully controlled than most people realize, and the difference between a reliable reading and a misleading one often comes down to where and how the sensor is placed.
Why Sensor Placement Matters More Than the Sensor
A thermometer sitting in direct sunlight can read 10 to 20 degrees higher than the actual air temperature. Sunlight heats the sensor itself, and reflected heat from pavement, buildings, or bare soil adds even more error. To avoid this, meteorological stations use a standardized shelter called a Stevenson screen: a white, louvered box designed in the 19th century specifically to isolate thermometers from “merely local influence,” particularly direct and reflected solar radiation.
The double-louvered walls allow air to flow freely through the box while blocking sunlight and precipitation. The box is painted white to reflect heat rather than absorb it. Inside, the sensor reads the temperature of the air passing through, not the temperature of any surrounding surface. This is why official weather stations are placed over grass, away from concrete and buildings. The goal is to measure the atmosphere, not the environment immediately around a parking lot or rooftop.
Height matters too. Standard placement is 1.5 to 3.5 meters above ground. Too close to the ground and you pick up radiant heat from the soil. Too high and you lose the reading that represents conditions at human level.
How Electronic Sensors Detect Temperature
Modern weather stations don’t use liquid-in-glass thermometers. They use electronic sensors that change their electrical resistance as the surrounding air gets warmer or cooler. The two main types are resistance temperature detectors (RTDs) and thermistors, and professional stations favor RTDs for outdoor use.
An RTD is built around a thin winding of platinum wire wrapped around a ceramic or glass core. Platinum is the preferred metal because it responds to temperature changes in a predictable, stable way over many years. As air temperature rises, the platinum’s electrical resistance increases in a precise, linear pattern. The station’s electronics measure that resistance and convert it to a temperature value.
Thermistors work on the same resistance principle but use a small bead of metal oxide semiconductor instead of platinum wire. They’re more sensitive to small temperature changes, which sounds like an advantage, but they’re also more fragile and less stable over time. For the rugged, long-term demands of an outdoor weather station, RTDs win on durability.
To ensure these sensors stay accurate, they’re calibrated against reference standards. For routine weather observations, instruments need to be accurate within about 0.5 to 1.0°C. Achieving that requires the sensor itself to be calibrated to a tighter tolerance of 0.1°C or better, because small errors in the reference instrument compound into larger errors in daily readings.
What Happens at an Automated Weather Station
Most official temperature readings in the United States come from the Automated Surface Observing System (ASOS), a network of stations located primarily at airports. These stations run continuously without human observers, sampling conditions around the clock.
Temperature is just one of many measurements the ASOS takes simultaneously. Each station includes sensors for barometric pressure, dew point, wind speed and direction, visibility, precipitation, cloud height, and even lightning. The temperature and dew point sensor sits inside a shielded, aspirated housing, meaning a small fan actively pulls air across the sensor to ensure it’s reading fresh ambient air rather than stagnant air that might have warmed inside the enclosure.
The station samples temperature frequently and reports updated observations, typically every minute for internal records and at regular intervals for public weather reports. The highest possible temporal resolution is maintained so that daily highs and lows reflect actual peaks and valleys rather than averages that smooth out brief extremes.
Satellite Temperature Measurement Works Differently
Satellites don’t measure air temperature the way ground stations do. Instead, they detect infrared radiation emitted by the Earth’s surface and use that to estimate what’s called land surface temperature (LST). This is essentially the “skin” temperature of whatever the satellite is looking at: soil, vegetation, pavement, rooftops, or water. It penetrates only about 12 micrometers deep, so it’s truly a surface reading.
This is not the same thing as the air temperature reported in your weather forecast. On a sunny afternoon, a dark asphalt road might have a surface temperature of 140°F while the air two meters above it reads 95°F. Satellite LST correlates with air temperature but can differ significantly depending on land cover and sky conditions. During daytime, satellite readings tend to run higher than air temperature. At night, the two converge much more closely. One comparison study at a climate reference site found that nighttime air temperature explained 98% of the variance in surface temperature, with a difference of only about 0.8°C.
Satellite data is most useful for tracking temperature patterns over large areas, monitoring heat islands in cities, and filling in gaps where no ground stations exist. But the temperature you see on your weather app comes from ground-based sensors, not satellites.
Air Temperature vs. “Feels Like” Temperature
The number on your weather app labeled “feels like” is not a direct measurement. It’s a calculation that combines the actual air temperature with other conditions your body responds to, mainly wind and humidity.
When the air temperature drops below 50°F and the wind is blowing faster than 3 mph, the reported “feels like” value is a wind chill calculation. Wind strips heat from your skin faster than still air does, so a 30°F day with a 15 mph wind feels significantly colder. The formula factors in both temperature and wind speed to estimate how fast exposed skin loses heat.
In warm weather, the calculation flips to a heat index. When the air temperature is above 80°F, humidity becomes the dominant factor because your body cools itself through sweat evaporation. High humidity slows that evaporation, trapping heat. The heat index combines temperature and relative humidity to produce a value that represents how hot it actually feels to a human body. A 95°F day at 50% humidity can feel like 107°F.
Both calculations start with the same measured air temperature from the same shielded, ventilated sensor. The “feels like” number is a derived value designed to reflect human comfort, not a separate measurement of the atmosphere.
Why Your Backyard Thermometer Disagrees
If your porch thermometer reads five or even ten degrees higher than the official temperature, the station isn’t wrong. Home thermometers are rarely placed in ideal conditions. A sensor mounted on a south-facing wall absorbs reflected heat from the building. One sitting on a deck picks up radiant heat from the wood. Even a shaded sensor near a concrete patio will read high on a summer afternoon because the concrete radiates stored heat.
To get a reading closer to official conditions at home, place your thermometer in a shaded, open area with good airflow, over grass, and away from walls, pavement, and other heat-absorbing surfaces. A simple homemade radiation shield (even a stack of white plastic plates with gaps for ventilation) makes a noticeable difference. You still won’t match professional accuracy, but you’ll eliminate the most common sources of error that can throw readings off by double digits.