Explainer: The Plum Rain Season of East Asia

By Ned Kelly

The Explainer is where we explain an aspect of Chinese life. Simple. So now you know.

The East Asian rainy season or meiyu (literally plum rain), which usually starts in June and can last all the way into August, is the result of a weather front (a boundary separating two masses of air of different densities) that is created when the moist air over the Pacific meets the cooler continental air mass.

When the moist air is cooled, the water within it condenses into drops heavy enough to be pulled down by gravity and, well, raindrops keep falling on our heads.

This front moves back and forth as the cool and warm air masses battle it out, ending only when a warm air mass from the south, associated with the subtropical ridge, is strong enough to push the front north and away.

Be careful wishing for that subtropical ridge, though: not only does the mercury soar to uncomfortable levels; most tropical cyclones form on the side of it, which means monsoon season.

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