By contrast, it's happened five times since 2000. Only four times in the first 90 years of the record did the region experience a spring (March-May) during which 25% of the region experienced extreme 1-day precipitation. NOAA image using data from NCEIĪs the graph above shows, the percent of the Ohio Valley region experiencing extreme one-day rainfall events in any individual spring has been elevated during the past thirty years compared to the twentieth century. A larger proportion of our precipitation across the Ohio Valley region is coming from single day events in more recent years than what we've observed historically. The dark line represents a five-year running average. The percent area of the Ohio Valley experiencing springtime (March-May) one-day extreme precipitation totals from 1910-2020. And according to NOAA’s Climate Extremes Index, the Ohio Valley region has seen an increase in extreme precipitation in spring between 19. The Southeast has seen an 18% increase in heavy rainfall days (defined as the top 1% of all rainfall days) from 1986-2016 when compared to 1901-1960. But extreme precipitation events are on the rise across much of the country since the beginning of the 20 th century.
Of course, flash flooding has happened and will happen without any help from global warming. Any trend in extreme precipitation events? In the end, peak rainfall amounts that had at most only a 1% chance of occurring in any given year (a 1 in 100 year event) fell this past weekend in Tennessee.
At the State Fairgrounds in Nashville, Browns Creek jumped over nine feet in less than six hours, reaching levels not seen since 2010. The Harpeth River at Franklin, just south of Nashville, rose 25 feet in around 15 hours. Much of this rain ran off into nearby creeks, which quickly overtopped their banks, flooding roads and homes. It was only surpassed by the epic rains and flooding that occurred in May of 2010. Over the course of the entire event, March 27-28, over seven inches of rain fell, the fourth largest two-day rainfall event in city history. In Nashville, 5.75 inches fell on March 27, setting a record for the wettest March day for the city. This constant onslaught caused a large swath of the state to receive 4-8 inches of rain, much of it falling in a twelve-hour period on March 27. It seemed like whenever one storm moved through, another was waiting in the wings to take its place. Starting on March 27 and lasting through the beginning of March 28, a storm system that was responsible for over 20 tornado reports, most of which were in Texas, moved across the Tennessee Valley bringing a steady stream of thunderstorms and heavy rain. This map shows 24-hour rainfall totals from storms over the Southeast on March 27, 2021, based on PRISM data from Oregon State University. If you click on the 'upstream gauge' or 'downstream gauge' links you can navigate to other gauge measurements of the river.A steady flow of thunderstorms dropped 4-9 inches of rain across a large swath of Tennessee in late March, causing widespread flash flooding.
The site includes a Google Map showing the location of the gauge reading. At the time of writing the NOAA shows the river level at nearly 51 feet (the major flood stage is from 45ft) and a flood warning is in place. You can view near real-time data for the Cumberland River in Nashville with the National Weather Service's Advanced Hydrologic Prediction Service. NOAA: Advanced Hydrologic Prediction Service Staff of the are working to keep the map up-to-date. The map shows the locations of shelters, missing person reports, fatalities and public transit cancellations. Nashville newspaper the has created a Google Map to show incidents of the Nashville flood. If you zoom in on Nashville and select the 'Road Condition' option you can view the currently flooded roads and Nashville road closures. The Tennessee Department of Transport's Smartmap uses Google Maps to show weather-related road conditions, construction/incidents, camera images and message signs for the state. Tennessee Department of Transport: Smartmap
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