While the heat and humidity are easier to understand, those “pulse-severe,” localized storms are a bit more complex.
In general, storms develop quite easily in the Carolinas in the summer due to hot temperatures near the ground, cooler air above the ground and abundant tropical moisture. Once a column of air heats up it starts to rise, due to being a bit warmer than the surrounding environment. As that column of air rises it begins to cool, allowing the abundant moisture to condense and collect into raindrops.
Over time, sometimes within 15 minutes, those rain droplets continue to grow in size and weight. As raindrops become heavier, they begin to fall and evaporate slightly on the way down. Between the formation and evaporation of raindrops, the column of air cools and begins to sink, due to now being cooler than the surrounding environment.
That column of air continues to cool as more raindrops develop and evaporate. This persistent cooling process allows the column of air to sink faster and faster as its central temperature gets cooler and cooler than the surrounding environment.
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