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A look at weather extremes and the big-picture climate connections.

Southeast Rainfall More Variable as Climate Warms

(Originally published on Washington Post's Capital Weather Gang blog)

In recent years the southeastern U.S. has had a string of summers with unusual amounts of rainfall. There was the withering drought in 2007, during which Georgia Governor Sonny Perdue famously held a prayer service for rain. This eventually worked — albeit too well. Late last summer the drought-stricken region was hard hit by record flooding.

A new analysis of six decades of weather and climate data finds that such extreme summers are becoming more common in the region, due to shifting atmospheric steering currents that appear to be related to manmade global warming.

The study, published in the early online edition of the Journal of Climate, investigates a key driver of summertime weather in the Southeast — the Bermuda High, referred to in the study as the "North Atlantic Summertime High" or "NASH." This High Pressure cell is typically centered in the vicinity of Bermuda, and often acts as a heat pump along the eastern seaboard, drawing warm and humid air up the coast throughout the summer. (You have the Bermuda High to thank for many of our summer heat waves in Washington).

By analyzing precipitation, wind, and humidity observations, along with data of the height of pressure surfaces aloft, the researchers found the western extent of the High pressure ridge has crept closer to the continental U.S. in recent decades, at the rate of 1.22 longitudinal degrees per decade. During that same period, the High has also grown stronger, and rainfall has grown much more variable from one summer to the next.

Read the full article at Washington Post's Capital Weather Gang blog.

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