The goal is to measure the air, not the sun
A weather sensor must be shaded and ventilated
A thermometer in direct sunlight absorbs solar radiation and reports the temperature of the heated instrument, not just the surrounding air. Official stations shield the sensor from sun and precipitation while allowing outdoor air to flow around it. White, reflective shields reduce absorbed radiation; louvers and sometimes a fan provide ventilation.
This does not mean a sunny patio “feels” no hotter. Your skin, clothing and nearby surfaces also absorb radiation. The standard measurement isolates air temperature so readings can be compared from one station and decade to another. The feels-like temperature guide covers the separate human-exposure question.
The standard weather-station setup
| Feature | Typical practice | Error it reduces |
|---|---|---|
| Radiation shield | White, reflective, louvered enclosure | Direct and reflected solar heating |
| Height | About 1.25–2 m (4–6.5 ft) above ground | Strong temperature gradients close to the surface |
| Ground below | Representative natural surface, often short grass | Heat radiated by roofs or pavement |
| Clearance | Away from buildings, exhausts and large obstacles | Local heat sources and blocked airflow |
| Ventilation | Natural airflow or fan aspiration | Heat building up inside the shield |
Why your car, phone and backyard disagree
A parked car’s sensor may be warmed by the engine, roadway and still air. A wall-mounted home sensor can absorb heat from brick or reflected afternoon sun. Phone weather apps usually show a station or model estimate, not a thermometer inside the phone. Each can differ from an official site without any device being “broken.”
Distance and elevation matter too. A coastal station, hilltop airport and sheltered valley can experience different air masses at the same moment. On calm nights, the air close to grass may be several degrees colder than the standard-height reading; our inversion guide explains the layering.
How to place a useful thermometer at home
- Use a purpose-built radiation shield in a location with free airflow.
- Keep it away from walls, concrete, asphalt, dryer vents, air conditioners and grills.
- Avoid overhanging trees that create a separate damp, sheltered microclimate if your goal is a broadly representative reading.
- Mount it near standard eye height over representative ground and keep the setup unchanged if you want to compare seasons or years.
Perfect official siting is rarely possible in a small garden. Consistency and a written note about the location are more useful than moving the sensor repeatedly to chase agreement with an app.
Accuracy, precision and representativeness
Accuracy is closeness to the true value; precision is repeatability or display resolution; representativeness asks whether the site describes the place you care about. A sensor can display 0.1°F increments and still be several degrees wrong because sunlight reaches it.
Before blaming calibration, compare two sensors side by side in the same shaded, well-ventilated environment long enough to stabilize. If a consistent offset remains, use the steps in our thermometer verification guide.
Why a phone, car or sunny wall can disagree with the weather station
An official air-temperature sensor is shielded from direct solar radiation and ventilated so surrounding air can reach it. A car sensor sits near a road and engine, a wall sensor exchanges heat with the building, and a phone usually obtains a remote weather observation rather than measuring outdoor air itself.
Differences can therefore be real without any device being broken. Pavement and walls heat the nearby air, elevation changes temperature, and a shower can cool one neighborhood while another stays dry. Observation time matters too: a station’s reported daily high is not necessarily the temperature at the moment an app opens.
For a useful home comparison, shade the sensor, allow airflow, keep it away from large surfaces and compare synchronized readings. Record location and height. The goal is not to force the home device to equal a distant airport, but to understand what each instrument is actually sampling.