Definition
The process by which liquid water changes into water vapor and enters the surrounding air. Evaporation absorbs heat from the liquid and the surrounding environment, producing a cooling effect. The rate of evaporation depends on temperature, humidity, wind, and the amount of exposed water surface.
Plain English
Water turning into invisible vapor and mixing into the air. As it does, it pulls heat out of whatever it leaves behind, which is why wet things feel cool as they dry.
Context Anchor
Seen in weather discussions about moisture, humidity, clouds, fog, and temperature changes near the ground.
Derivation
From the Latin evaporare, meaning 'to disperse in vapor.' The 'e-' part means 'out of,' and 'vapor' means 'steam' or 'mist' — so literally, 'to go out as vapor.' That captures the idea well: water leaving the liquid and drifting away as gas.
Why Pilots Care
Evaporation rates control how much moisture the air holds, which influences visibility, fog, cloud bases, and the likelihood of carburetor icing or reduced performance.
Analogy
A wet shirt feels cool as it dries because water is evaporating from it and taking heat with it. The same basic process happens when water evaporates from lakes, wet ground, or rain-soaked surfaces.
Grounding Statement
Step out of a swimming pool on a warm day and you feel cold, even though the air hasn't changed. That chill is evaporation pulling heat off your skin as the water turns to vapor.
Intuition Check
Evaporation is not the same as boiling; water can evaporate at normal outdoor temperatures. Evaporation means liquid water is changing into water vapor, even if you cannot see it happening.
Example Sentence 1
Evaporation from the wet runway added moisture to the air and contributed to the patchy fog that formed after sunset.
Example Sentence 2
Pilots watch evaporation rates when estimating how long morning dew will take to clear before an early departure.