Weather Station Data Explained: A Practical Glossary

A personal weather station reports a dozen numbers at once, and they are not equally useful. This glossary explains what each reading actually measures, how the sensor produces it, and which number to watch for a given question, with links to a deeper guide on each topic. Bookmark it as the index to the whole weather-data series.

Temperature: the easiest reading to get wrong

Air temperature seems like the simplest measurement on the station, and it is the one most often ruined by siting. A sensor in direct sun, over asphalt, or too close to a wall reads high, sometimes by several degrees. If your afternoon readings look inflated compared with nearby stations, work through why a weather station reads too high and the siting guide: radiation shielding, height, and surface underneath matter more than the sensor's spec sheet.

Dew point vs relative humidity

Relative humidity is the percentage of moisture the air currently holds relative to the maximum it could hold at its present temperature, which is why it swings all day while the air mass never changes. Dew point is the temperature to which air must cool before it saturates, so it measures the actual moisture present and is the number that predicts mugginess, fog, and condensation. As a rule of thumb, dew points below 16 °C (60 °F) feel comfortable and above 21 °C (70 °F) feel oppressive. The full explanation, including why 90% humidity can feel crisp, is in dew point vs humidity.

Heat index, wind chill, and apparent temperature

These "feels like" numbers are computed, not measured. Heat index is a derived temperature combining air temperature and humidity for warm conditions; wind chill is the equivalent for cold conditions, combining temperature and wind speed; apparent temperature blends both with solar input. They are useful summaries for visitors, but remember their inputs: a badly sited temperature sensor produces a misleading feels-like value too.

Barometric pressure and the 3-hour trend

Barometric pressure is the weight of the atmosphere above the sensor, and the pressure trend is its direction and rate of change over the previous three hours. The trend matters far more than the absolute value: a steady fall of a few hectopascals over three hours usually announces an approaching system, and a fast fall announces it loudly. Stations also reduce the raw reading to sea level so neighbouring stations are comparable. How to read rising, falling, and steady patterns is covered in barometric pressure trends.

Wind: sustained speed vs gusts

Sustained wind is wind speed averaged over a fixed period, often 2 or 10 minutes; a gust is a short peak lasting seconds. Forecasts usually quote sustained wind, while damage thresholds and exposed structures care about gusts, which can run 30-50% higher. If your station's wind numbers look low compared with the forecast, anemometer height and obstacles are the usual cause. The differences, and what counts as a "high" gust, are in wind gust vs sustained wind.

Wind direction and the wind rose

A single wind-direction reading is nearly noise; the pattern over time is the signal. A wind rose is a circular chart that stacks up how often wind blows from each direction, and how strongly, revealing your site's prevailing winds and its sheltered sectors at a glance. Reading one takes about a minute to learn: see what a wind rose is and how to read it.

Rainfall and the tipping bucket

A tipping bucket is a small see-saw inside the rain gauge that flips each time a fixed amount of water has fallen, typically 0.2 mm on metric Davis gauges, and the station simply counts the tips. That design is robust, but it means very light drizzle may never fill a tip, heavy downpours can slightly undercount, and a clogged funnel silently reports drought. How the mechanism works, and how other gauge types compare, is in how weather stations measure rainfall.

Solar radiation and UV index

Solar radiation is the total sunlight power reaching the sensor, reported in watts per square metre, and it drives derived values like evapotranspiration and apparent temperature. The UV index is a separate health-oriented scale for ultraviolet intensity, where 0-2 is low and 8 and above is very high. The two usually rise and fall together but are not interchangeable; thin cloud can cut solar wattage while UV stays significant.

Air quality: AQI vs EAQI

PM2.5 and PM10 are airborne particles smaller than 2.5 and 10 micrometers respectively, measured in micrograms per cubic metre by a particulate sensor such as the Davis AirLink. The AQI and EAQI are index scales that translate those concentrations into a health category. The United States AQI and the European EAQI use different breakpoints and different colour scales, so the same air can be "Moderate" in one and "Good" in the other. Which index your site should show, and how the two map to each other, is explained in AQI vs EAQI.

Frost prediction

Frost is ice that forms when a surface cools to or below freezing, and predicting it means reading several numbers together: a clear sky, light wind, and a dew point near or below freezing set the stage, and the temperature falling toward that dew point overnight closes the deal. Your own station is genuinely better at this than a regional forecast, because frost is intensely local. The method is in how to predict frost with a weather station.

Derived values: what the station computes rather than measures

Derived values are numbers your station calculates rather than measures. If you want the formal meteorological definition of any term on this page, the US National Weather Service glossary is the reference professionals use. Beyond feels-like temperatures, stations and software derive cloud base estimates from temperature and dew point, evapotranspiration from solar input and wind, and daily records from the raw stream. Derived values are honest as long as you remember the chain: every one of them inherits the errors of the sensors underneath.

Common questions

Which numbers should a beginner actually watch?

Dew point for comfort and overnight risk, the 3-hour pressure trend for incoming weather, and gusts rather than sustained wind for "was it stormy". Those three answer most day-to-day questions; the rest add depth once the basics feel familiar.

Why do my readings differ from the official station in town?

Distance, elevation, and siting. Official stations follow strict siting standards over grass in open terrain; your garden has walls, trees, and pavement. Differences of a degree or two in temperature and large differences in wind are normal and do not mean either station is broken.

Where can I see all of this on a live site?

A Pro Weather station site shows every reading in this glossary, live and with permanent history: current conditions, dew point, pressure trend, wind rose, rain, UV, solar, and air quality when the hardware reports it. The tabs and panels guide shows how it fits together.