Nationwide, the weather pattern has been “stuck” in more-or-less the same configuration for the past two weeks, with warm conditions dominating the southeast and persistent cold and wet weather across the Great Plains and Northwest. In between, a strong jet stream from Texas to the Northeast has brought a series of storms through the mid-South and into the Ohio River valley, with each storm bringing greater and greater amounts of moisture. The current flooding episode began with a light-to-moderate rain event across the Tennessee Valley on February 15-17, with generally 1-3″ falling across the region during this time. The saturation of soils began to compound as a second storm formed across the mid-South on Feb. 19th, producing an additional 2-4″ of rain across Arkansas, northern Mississippi and Alabama, and much of Tennessee. By far the largest and most problematic storm came just two days later, with an axis of heavy rain and thunderstorms stretching from the Mississippi-Arkansas border through northeastern Tennessee from the evening of the 21st through the morning of the 24th. Many locations in south-central Tennessee and northern Mississippi received 2-5″ of rain per day for up to 3 days, with reported 3-day totals of 7-9″ with nearly 10″ in isolated locations. Over the course of the last week (ending this morning, February 25th), totals have been as high as 12-14″ across parts of northern Mississippi, northwest Alabama, and south-central Tennessee, as depicted by our preliminary MetStorm Live analysis in Figure 1. This has produced the wettest February on record in parts of Tennessee, including the cities of Nashville and Crossville.

MetStormLive 20190225 7day rainfall TN valley

Figure 1. Total rainfall over the 7 days from the morning of 18 Feb 2019 through the morning of 25 Feb 2019 across the Tennessee Valley and adjacent areas.

The result of all this rainfall is extremely high reservoir levels in the Tennessee Valley Authority’s system of dams (see their updates on the storm at their website). As addressed in the TVA’s news release, they are expecting near-record flooding for a string of five cities along the middle and lower Tennessee River, including Decatur and Florence in Alabama and Savannah, Clifton, and Perryville in Tennessee. As stream gauges at Savannah and Perryville indicate, major flooding is well underway at these locations, will likely not peak until Tuesday-Wednesday, and will be very slow to fall as upstream reservoirs continue to make large releases (Figure 2). In both cases shown here, record crests are not forecast, but both are expected to be among the top 5 recorded water levels at each site.

stream gauges

Figure 2. Streamflow plots showing the observed levels (blue curves) and forecast river levels (purple dots/line) for the Tennessee River at Savannah, TN (left) and Perryville, TN (right).

As part of its efforts to mitigate major flooding events such as this one, the TVA has previously worked with partners MetStat, MGS Engineering, and RTI International on developing a hydrologic hazards assessment for the many dams they operate within the Tennessee River watershed (for a brief summary, see our Project Portfolios page). Such studies help hydrologists and engineers to prepare their infrastructure and operations to minimize the impact of damaging flood events. We wish everyone dealing with the consequences of this flood event the best and hope that our work has helped to prevent even worse outcomes across the Tennessee Valley.

For more on our watershed precipitation frequency services and hydrologic modeling support services, please explore the links provided. Be sure to subscribe to our blog and follow our social media feeds for more updates on major storm events across the country as well as announcements about our exciting new innovations.