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Daryl Ritchison, WDAY, Published June 14 2012

Weather Talk: Drier wind pattern started in August largely continues

One of the reasons often given for the persistence of above-average precipitation over the past two decades has been that wet begets wet. In other words, that the wet soil has allowed for more evaporation, which in turn caused it to rain more.

The cycle continued year after year. This is referred to as a positive feedback loop, in which a change in one variable – soil moisture – reinforces the original process, rainfall. Although there is some truth to this, it has only been a minor player. For example, last summer was very wet until Aug. 6, but then the rain stopped and never returned.

What changed was the low-level wind pattern. Almost all our summer moisture comes from the Gulf of Mexico, and subtle changes in moisture advection from the south can radically alter how much moisture this area receives.

This season, so far, has largely continued the drier wind pattern started last August.

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