Flash flood watches stretch more than 500 miles, from central Mississippi to West Virginia, as early spring soakers target the Ohio and lower Tennessee valleys. A continuing parade of storminess is expected in the days ahead and, perhaps, beyond.
The flooding is already underway, thanks to wet conditions over recent days. Some spots have been wet through much of the winter. As an example, a flash flood warning was issued for Davidson County, Tenn., this morning, including the Nashville metro area. This round of heavy rain is expected to wane in the afternoon hours.
“We’ve already seen one to three inches across middle Tennessee,” said Faith Borden, a meteorologist with the National Weather Service in Nashville. “We’re expecting another one to two inches this afternoon and evening. Then we’ll dry out before we get another two or three inches this weekend.”
It’s been a wet month for Music City. Nashville set a rainfall record on Feb. 6 after picking up four inches in 24 hours. And in the past three days, 2¼ inches have fallen. “We’re at our seventh-wettest February on record for rainfall,” Borden said. “I’m pretty sure we could definitely move up to at least third or fourth.”
Another drenched location is Louisville. Louisville sits at 5.1 inches for the month, which is more than two inches above where it should be at this point. The Kentucky city is bracing for roughly five additional inches Saturday and Sunday. The National Weather Service in Louisville is warning that “copious rainfall will agitate ongoing flooding and create new flooding.”
The seemingly endless rains are thanks to a stalled front draped along the Interstate 40 corridor, which more or less cuts northern and southern Tennessee in half. Areas of heavy rain shift toward the Appalachians today into tonight, making a run in places such as Atlanta and Birmingham, Ala., with sporadic downpours before falling apart.
Over the next few days, another approaching buckle in the jet stream should eventually reawaken the front, with surges of moisture riding along it like rail cars on a train track. Pine Bluff, Ark., along with Memphis, Nashville and Jackson, Tenn., look to be ground zero for the halted front’s deluge. Surrounding areas such as Bowling Green, Ky., also are likely to get soaked.
It’s not out of the question that one-week rain totals approach 10 inches in a few spots.
In its Wednesday morning discussion, the Weather Prediction Center referenced anomalously high groundwater content as a possible factor exacerbating flood concerns.
“The risk areas reflect the higher ground moisture content and reduced flash flood guidance values in the central to southern Appalachians and adjacent valley areas of eastern Kentucky and Tennessee,” it wrote. In other words, the ground is already saturated — and it can’t handle much more water. That will lower the threshold of rainfall needed to create flash flood conditions.
A large swath of the South and surrounding regions are above the 90th percentile for February ground water content. Most of the Mid-Atlantic and southern New England are in the 99th percentile!
Despite being far wetter than average, this surprisingly marks a decline in ground water for Georgia, Alabama, Mississippi and Louisiana since this time last month. Much of that water is left over from heavy rains earlier this winter. Meridian, Miss., recorded twice its average monthly rainfall in December — 10.26 inches!
In addition to flooding rain, the weekend system will present a risk of severe thunderstorms.
The Storm Prediction Center has outlined a broad area of concern, eyeing the Ozark Plateau and lower Mississippi Valley as spots for a vigorous squall line to develop. Isolated storms ahead of the line could present a tornado threat, while a few short-lived spin-ups also are possibly embedded within the line itself. Damaging winds to 60 mph also may accompany the line as it blasts through Saturday afternoon and night, fortunately bringing an end to that round of torrential rains.
After that, there are signs that the pattern may continue to deliver more wet weather. A cold shot from the north may ease the concern later in the month, at least for a while. Starting off so wet and heading into a wet time of year, it seems likely that we’ll revisit this in the future.