Weather System & Rainfall Analysis
Here is the set up for a weather system moving across the region. Take a look at the “Detached Upper Low” as indicated by the red “L.” This low will help (temporarily) break down the upper ridge of high pressure that has brought record levels of heat to the Southeast U.S. Note the enhanced clouds ahead of a cold front that will push across the region over the next day or so.
If we take a closer look at some of the smaller-scale features of this system, we see that moisture is pooling, or converging, along southern sections of the cold front. In the following image, blue contours indicate areas of highest convergence of moisture. The red arrows indicate streamlines of low-level flow. If you look closely, you will see that winds are flowing directly from the Gulf of Mexico into far southern sections of this area of precipitation. The area of heaviest rainfall is closely aligned with the strongest area of inflow from the Gulf.
The SERFC is calling for significant rises on rivers within the area of heaviest rainfall – but only isolated main stem river flooding. Why? Take a look at the following image showing 6-hour Flash Flood Guidance. The extensive area of blue over the Southeast U.S. represents a 6-hour guidance value of 4 inches of rainfall, or more. Values are somewhat lower over far northern Alabama and Georgia, and parts of North Carolina. Note the red/green spots in Mississippi. In this region, it would only take an inch or so of rain to produce a more significant response on rivers. Thus, this is the area where we foresee the best chance for more significant rises and possibly isolated flooding.
Elsewhere, especially over the core of the drought, South Georgia and surrounding areas, this rainfall will be quite welcome.
This front will drop temperatures a bit, but it looks like the upper ridge will again build after a few days with above-normal temperatures into the foreseeable future.