Parts Of Southern Georgia Saw 7 Inches Of Rain In Just Three Hours On Tuesday

A large cluster of thunderstorms that popped up in southern Georgia on Tuesday evening produced more than 7.00 inches of rain in just a couple of hours, prompting a flash flood warning as local waterways and storm sewers were inundated by the abrupt surge of water. The sudden nature of the storms highlights the flooding risk that summertime thunderstorms can pose in the moisture-laden southeastern United States.

Folks who live in the southeast are no strangers to a drenching afternoon thunderstorm. It’s not uncommon for a thunderstorm to pop up and drop a quick inch or two of rain before moving on an hour later. The storms north of Valdosta, Georgia, however, are an example of how quickly things can get serious when your run-of-the-mill summertime thunderstorms sit in the same spot for too long.

The cluster of thunderstorms that put down the torrential rain were the result of converging outflow boundaries. An outflow boundary is the rush of cool air that descends out and away from a thunderstorm. Outflow boundaries often act like little cold fronts that scoop up unstable air ahead of them and trigger the development of more thunderstorms as the afternoon wears on. This domino effect can continue until the unstable air is exhausted—usually around sunset.

Outflow boundaries were responsible for the flooding rains over southern Georgia on Tuesday. Imagery from the Valdosta radar showed multiple outflow boundaries colliding almost head-on across the counties north of Valdosta. A cluster of thunderstorms bloomed when the boundaries collided and the unstable air had nowhere to go but straight up.

Radar-estimated rainfall amounts on Tuesday evening. Source: GREarth/AllisonHouse

Since there weren’t any prevailing boundaries or strong steering currents to drive the storms out of the area, they just sat and poured over the same communities for several hours at a time as they very slowly drifted toward the south. A weather spotter near Weber, Georgia, reported 5.81 inches of rain
between 5:54 PM and 7:54 PM. NWS Tallahassee reported on Twitter that one community—possibly that same weather spotter—saw more than 7.00 inches of rain by the time the storm wound down. Radar estimates indicate that several counties saw 5-7 inches of rain during the storm.

The Weather Prediction Center warns that there’s a chance for more flash flooding across coastal sections of Georgia, South Carolina, and southeastern North Carolina on Wednesday. It’s hard to say who will see the heaviest rains, but any thunderstorms that pop up in the region have the potential to produce lots of heavy rain in a short period of time.

[Radar Imagery: GR2A/Gibson Ridge]

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