Weather APIs return dozens of data points, from temperature and humidity to barometric pressure and wind vectors. Understanding what each metric means—and how they relate to each other—is essential for building useful weather features.
Temperature Metrics
Weather APIs typically return multiple temperature values. The actual temperature (tempC/tempF) is the measured air temperature, while "feels like" (also called apparent temperature) factors in humidity and wind to reflect how the temperature feels to humans. High humidity makes warm temperatures feel hotter because sweat evaporates slower. Wind chill makes cold temperatures feel colder due to increased heat loss from skin.
Humidity and Dew Point
Relative humidity (expressed as a percentage) indicates how much moisture is in the air relative to the maximum it can hold at that temperature. 100% humidity means the air is saturated. Dew point is the temperature at which air becomes saturated—a dew point above 65°F (18°C) feels muggy, while below 50°F (10°C) feels dry. For user comfort features, dew point is often more useful than relative humidity.
Barometric Pressure
Atmospheric pressure (measured in millibars or inches of mercury) indicates weather patterns. Rising pressure generally means improving weather; falling pressure suggests storms approaching. Standard sea-level pressure is 1013.25 mb (29.92 inHg). Pressure changes of 3+ mb in 3 hours often indicate significant weather changes.
Wind Data
Wind is described by speed and direction. Direction indicates where wind is coming FROM (a "north wind" blows from north to south). Wind gusts are brief increases in speed, often 30-50% higher than sustained wind. For aviation, marine, and outdoor activity apps, both sustained wind and gust data are critical.
Precipitation
Precipitation data includes probability (chance of rain), amount (in mm or inches), and type (rain, snow, sleet). Accumulation forecasts help with planning—1 inch of rain over 24 hours is light; the same amount in 1 hour causes flooding. Snow ratios vary: light fluffy snow may be 15:1 (15 inches snow per 1 inch water), while wet snow is closer to 5:1.