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cold front vs. warm front

cold front

[kohld fruhnt] / ˈkoʊld ˌfrʌnt /

noun

the zone separating two air masses, of which the cooler, denser mass is advancing and replacing the warmer.

warm front

[wawrm fruhnt] / ˈwɔrm ˌfrʌnt /

Meteorology.

a transition zone between a mass of warm air and the colder air it is replacing.