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Meteorology studies atmospheric structure, motion and the processes producing weather. Uneven heating generates pressure gradients, air motion transports heat and water vapor, and condensation or freezing releases latent heat. Rotation and surface friction help determine how that motion develops.

A weather station measures local conditions, while comparing observations over space reveals evolving atmospheric systems. Wind, temperature, relative humidity and pressure constrain different parts of the physical state; no one sensor completely describes it. Forecasts combine these observations with equations for fluid motion, energy and moisture. Climatology instead emphasizes statistics over longer periods, using many of the same physical mechanisms and observing systems.

The National Oceanic and Atmospheric Administration is a United States scientific agency whose observations and research cover the atmosphere and oceans. Its measurement products connect meteorology, climatology and ocean circulation, with a stated observing method and reference period needed to interpret each product.

For example, its Arctic Oscillation index projects a measured atmospheric field onto a specified spatial pattern, while a climatological normal summarizes a different kind of information: statistics over a defined reference interval.^[ref][ref] Neither product is a direct measurement of one universal scalar called climate.

A weather station is a set of instruments measuring atmospheric conditions at a specified site. A thermometer records temperature, a barometer records pressure, an anemometer records wind, and a rain gauge measures collected rainfall. Moisture observations may be reported as relative humidity or dew point.

Instrument exposure is part of the measurement. Direct sunlight can heat a temperature sensor above the surrounding air; nearby buildings alter wind; the height and averaging interval affect comparability. A long record therefore needs instrument and site metadata as well as numbers. Consistent observations support both immediate meteorology and the statistics used in climatology.