Flash Flood Emergency in Northern Lousiana: Over a Foot of Rain in 24 Hours

A Flash Flood Emergency has been declared in Northwest Louisiana, including the city of Shreveport, where over a foot of rain fell in just 24 hours, from Tuesday morning through Wednesday morning. At Shreveports's Barksdale Air Force Base, 13.16" had fallen as of 10 am EST Wednesday, and over 14 inches of rain fell just to the southeast of Shreveport near Bossier City. The heavy rains have led to numerous high water rescues and flooded homes and streets. Near Shreveport, up to 80 homes were flooded and a nursing home had to be evacuated due to rising waters, according to the Associated Press, and evacuations have been ordered in Greenwood, Haughton, Homer, Minden and Rayville, Louisiana. The flooding problems extend into Eastern Texas, where multiple bridges have been washed out northeast of Marlin, Texas. Although the heaviest rains moved out of Eastern Texas and Northern Louisiana late Wednesday morning, near-record levels of atmospheric moisture for this time of year--more than 200% of average--remain in place over the region, and renewed rounds of heavy rain are likely through Friday. Extreme flooding rains were spreading into Southern Arkansas on Wednesday morning, and rainfall amounts of a foot in 24 hours are possible there, as well. Additional major flash flooding over the next few days is also possible in Houston, San Antonio, Austin, Shreveport, Little Rock, Memphis and New Orleans.


Figure 1. Flooding in Bossier Parish, Louisiana on March 9, 2016 submerged some houses up to their roofs. Numerous water rescues were made Tuesday night as high water started to pile up in parts of Louisiana after heavy rainfall. (CBS News Correspondent @DavidBegnaud) 

Although flooding is the major concern from this slow-moving storm system, severe thunderstorms and a few tornadoes are also expected through Thursday in some of the same parts of the Lower Mississippi Valley and Gulf Coast. So, far, the storm had spun up three tornadoes since Monday. An EF1 tornado caused damage near Cool, Texas Monday evening, and an EF1 tornado touched down near Tolar, Texas, southwest of Ft. Worth Tuesday morning. An EF1 tornado also left a narrow path of damage in Stephenville, Texas early Tuesday. Severe thunderstorms hit the Ft. Worth, Texas region, with a 66 mph gust at the Ft. Worth Meacham Airport. Baseball size hail pounded Voca, Texas Tuesday evening, while hail to the size of golf balls covered the ground in both Evant and Jonesboro, Texas. Two drowning deaths have been attributed to the storm system: a man in Broken Bow, OK that drove across a flooded bridge and got swept away, and a man in a canoe on Dickinson Bayou near Hwy 3 in Dickinson, TX where the wind blew him into the water. Thanks go to wunderground members RitaEvac and Skyepony for this info.


Figure 2. Storm damage from early Tuesday in Frisco, Texas. (@NTXStrmTrackers/Twitter.com) 

A "cut-off" low is responsible
A large low pressure system (a "cut-off" low) has separated from the jet stream, and will stay parked over the U.S./Mexico border region during the next few days. The counter-clockwise flow of air around this low is bringing up plenty of warm, moisture-laden air from the tropics along the east side of the low, causing the heavy rains we've observed. By this weekend, when all of this rain has had time to flow into area rivers, expect to see several rivers crest at near-record flood levels. Sea Surface Temperatures (SSTs) are near average over the Gulf of Mexico, which will keep the amount of moisture available to this week's storms lower than would be the case if SSTs were unusually warm. However, the cut-off low has tapped into a moisture source in the deep tropics over the Eastern Pacific where SSTs are record warm. An "atmospheric river" of water vapor can be seen on satellite images extending from the record-warm El Niño-heated waters south of Mexico directly into the Southern U.S. This warm, moist air is very unstable, which will help contribute to severe thunderstorms with a few tornadoes over the Southern U.S. today through Friday.


Figure 3. Observed 24-hour precipitation for the period ending at 9 am EST Wednesday, March 9, 2016. Portions of northern Louisiana received over a foot of rain, and a large area of 8+" fell over portions of Eastern Texas and Northern Louisiana. Image credit: NOAA/NWS.


Figure 4. Lots more rain on the way: predicted precipitation for the 3-day period ending 7 am EST Saturday, March 12, 2016. Image credit: National Weather Service.

Jeff Masters