Definition
The amount of heat energy absorbed by a liquid as it changes into a vapor, with no change in temperature during the change of state. In the atmosphere, when water evaporates from oceans, lakes, soil, or precipitation, it pulls heat energy out of the surrounding air or surface, cooling it.
Plain English
The hidden cooling effect that happens when water turns into vapor. Evaporating water has to absorb heat from whatever is around it, so the surroundings get cooler.
Context Anchor
Seen in aviation weather discussions about moisture, temperature, evaporation, condensation, clouds, fog, and cooling air.
Derivation
Latent comes from the Latin latens, meaning 'hidden.' The heat is called 'latent' because it disappears into the water during evaporation without raising its temperature -- the energy is hidden inside the water vapor rather than felt as warmth.
Why Pilots Care
Controls how moisture enters the air, influencing fog, cloud buildup, and the strength of updrafts.
Analogy
Same effect you feel stepping out of a swimming pool on a warm day -- the water on your skin evaporates and you feel cold, even though the air temperature has not changed. The water is pulling heat off you to make the change from liquid to vapor.
Grounding Statement
When rain or mist evaporates into drier air, it takes heat from the surrounding air, so the air can cool even if no colder air has moved in.
Intuition Check
Do not read latent as meaning weak or unimportant. Here, latent means hidden: the heat is being used to change liquid water into water vapor, so it may not appear as a temperature increase.
Example Sentence 1
The latent heat of evaporation cools the air beneath a rain shaft as falling drops evaporate before reaching the ground.
Example Sentence 2
High humidity increases the latent heat of evaporation released when water vapor condenses inside a thunderstorm, feeding stronger updrafts.