Why Your Weather Station Reads Hotter Than the Airport

Your console says 31 °C. The airport 15 km away says 27. Before you open the calibration menu or order a new sensor, know this: the gap is almost never a faulty sensor. It is usually where and how the sensor is mounted — and occasionally your station is simply right about a genuinely warmer spot.

Why does my weather station read hotter than the airport?

The most common cause is siting, not the sensor. Sunlight heats the radiation shield and the air trapped inside it, nearby pavement and patios radiate stored heat upward, and light-colored walls reflect extra energy onto the sensor. A smaller share of cases is a real calibration offset — and sometimes your location genuinely is warmer than the airport.

Think of it this way: the sensor reports the temperature of the air that actually touches it. If that air has just passed over sun-baked concrete, or has been sitting inside a shield in full sun with no wind to flush it out, the sensor is measuring faithfully — it is just measuring the wrong air. That is why the fix is usually moving or shielding the sensor better, not adjusting it. Our weather station siting guide covers where to mount the sensor so it samples air that represents your area rather than your patio.

When is the reading too high? The timing tells you why

Watch when the gap appears before deciding what to fix. Radiation and surface errors follow the sun; a calibration offset never sleeps; urban heat shows up after dark. A week of comparing your charts against a nearby reference is usually enough to see the pattern clearly.

A steady, constant gap in all conditions is the one case where the sensor itself deserves suspicion — see how weather station sensors work for what is actually inside that shield and what can drift.

What does a radiation shield do, and why do official stations use fans?

A radiation shield blocks direct sunlight from hitting the temperature sensor while letting air flow past it. Standard shields are passive: stacked louvred plates that rely on wind for ventilation. Official stations instead use fan-aspirated shields that pull air across the sensor continuously, because passive shields read high in strong sun with little wind.

That weak spot — bright sun plus calm air — is exactly the condition of a summer afternoon. With no breeze to flush it, the air inside a passive shield warms above the true air temperature, typically by a degree or more in the worst conditions. Davis sells an optional 24-hour fan-aspirated radiation shield for the Vantage Pro2 that runs a solar-powered fan day and night, which is why fan-aspirated models consistently track closer to official readings on calm sunny days. Most hobby stations do fine with a passive shield in a good location; the fan matters most if your site is sheltered from wind or you care about matching official records closely.

How much heat do pavement and walls add?

Hard surfaces can add several degrees on a sunny day. Asphalt, concrete, patios, and gravel absorb solar energy and release it into the air directly above them — and keep releasing it well into the evening. A sensor mounted over or beside them measures that heated layer, not the general air temperature.

Walls make it worse in two ways. A light-colored, sun-facing wall reflects radiation straight onto the shield, and any wall stores heat during the day and radiates it back at night, which is why stations mounted close to a house often read warm around the clock. Roof mounts suffer a related problem: the roof surface itself bakes, and the warm air rises past the sensor. The general rule from siting standards is simple: the sensor should stand over natural ground, as far from hard surfaces and structures as your garden allows.

How do airports measure temperature?

Airport stations follow World Meteorological Organization siting standards: the sensor sits 1.25–2 m above level, open ground — short grass, not pavement — well clear of buildings, and inside an aspirated or well-ventilated shield. That combination is designed to measure air that represents the broader area rather than any nearby surface.

The details are laid out in the WMO Guide to Instruments and Methods of Observation (WMO-No. 8), and the US National Weather Service publishes similar siting guidance for citizen stations. It is worth reading those not because your garden can meet them — almost no home site can — but because they tell you what the airport number means: temperature over open grass, away from every heat source. If your sensor hangs over a courtyard, you are measuring something different by design.

When is your station right and the airport just far away?

Sometimes there is no error at all. Fifteen kilometers is enough distance for a real temperature difference of several degrees: coastlines run cooler on summer afternoons, valleys pool cold air at night, towns hold heat that open airfields shed, and a modest elevation change shifts temperature too.

Your station measures your garden — that is the whole point of owning one. A frost that never shows at the airport but blackens your seedlings is real, and your station is the instrument that catches it. One useful cross-check between sites: dew point varies more smoothly across a region than temperature, so if your dew point roughly matches the airport while your temperature runs high only on sunny afternoons, that points back to radiation error rather than a genuinely different air mass.

How do you verify whether your station is accurate?

Compare on heavily overcast, breezy days or at night. With no sun there is no radiation error and wind keeps the shield flushed, so a healthy, well-sited station should land within about a degree of a trustworthy nearby reference. If the gap vanishes in those conditions, your sensor is fine and your siting is the culprit.

If the gap persists on overcast windy nights, then you may genuinely have an offset — that is the moment to run a proper side-by-side check against a known-good thermometer and, only if drift is confirmed, dial in a correction. Our guide on how to calibrate weather station sensors walks through the reference checks and where offsets live in the Davis console and WeatherLink. Resist the urge to "calibrate" against the airport on a sunny afternoon: you would be programming a siting error into a healthy sensor.

How do you spot these patterns on your own site?

Diagnosing siting problems is much easier with history in front of you. On a Pro Weather site, the 24-hour and 7-day charts make the signature obvious: sharp afternoon spikes that relax after sunset point to radiation error, while a curve that runs uniformly warm suggests an offset. Because Pro Weather stores your full station history, you can also compare this July's overcast days against last year's to confirm a sensor is drifting rather than guessing from memory.

Common questions

Why is my weather station 5 degrees too high?

A gap that large almost always means direct sun or hot surfaces. Check whether the sensor sees sunlight through or around its shield, whether it sits over pavement, decking, or gravel, and whether a sun-facing wall is nearby. A genuine sensor fault of five degrees is rare; siting errors of five degrees over a hot patio are not.

Do I need a fan-aspirated radiation shield?

Not usually. A passive louvred shield in a good location — over grass, away from walls and pavement — performs well whenever there is any breeze. Fan aspiration pays off on calm, sunny sites, or if you want readings that track official stations closely. Fixing bad siting first is cheaper and matters more.

Are home weather stations accurate?

Yes — good ones are. Davis Vantage stations use factory-calibrated sensors whose specified accuracy is comparable to official equipment. The practical difference between a home station and an airport station is rarely the sensor; it is the siting. A well-placed home station produces data you can trust for years.

Should I trust my weather station or the weather app?

For your exact location, trust your station — the app shows a model forecast or an observation from a site kilometers away. But first verify your station on an overcast, breezy day against a nearby reference. Once siting is sound, your station is the ground truth for your garden; the app never was.