The combination of a slow-moving non-tropical storm and a weak tropical disturbance loaded with moisture will unleash torrential rain and raise new concerns for flooding over the south-central United States into this weekend.
Moisture was already streaming northward from the upper Texas coast to Mississippi during Wednesday morning and will continue for several days over part of the lower Mississippi Valley.
Radar shows heavy rainfall dousing the Texas coast on Wednesday, June 5, 2019. (AccuWeather Interactive Radar)
Hourly rainfall of 1 to 3 inches can occur with daily rainfall averaging 3 to 5 inches.
However, there is the potential for some areas of the Interstate 10 and 20 corridors to receive a foot or more of rain from the multiple-day event that may last through the weekend.
Both Wharton and Palacios, Texas, received 8 inches of rain in less than 12 hours Wednesday.
Rainfall of this magnitude will trigger street and poor drainage area flooding, initially. Motorists should be prepared for road closures, substantial delays and the need to alter their routes. To drive through flooded roadways is extremely dangerous.
Cities such as Houston and Beaumont, Texas, and New Orleans, Lake Charles and Baton Rouge, Louisiana, will be at risk for inundation in some neighborhoods.
Some small streams and bayous will flood and ultimately trigger river flooding in areas that have not had such problems recently.
Home and property owners prone to flooding should be prepared to move valuables and seek higher ground.
To complicate matters, heavy rainfall over the Central states and melting snow from the Rockies has created a surge of water from the Missouri and Arkansas rivers that is emptying into the Mississippi River and flowing southward.
Over the lower part of the Mississippi Valley, this surge of water may occur at nearly the same time that heavy rain falls.
The combination thereof could result in record-challenging high water on the lower Mississippi River, especially where the water levels are not mitigated by spillways toward the middle and into the latter part of June.
Official forecast levels from Wednesday could be underdone over part of the Southern states along the Mississippi and other rivers depending on how far inland torrential rain occurs.
The spillway would be overtopped if not opened with the anticipated level of water. The release of water at the spillway and the Old River structure diverts some water from the main stem of the Mississippi River and creates flooding in the Atchafalaya River Basin.
The back edge of the heavy rain is forecast to make slow eastward progress this weekend.
Much of eastern Texas should be in the clear from rain by Saturday. However, runoff from rains through Friday will continue to cause flooding problems.
It may take until Monday or Tuesday before the rain departs the lower Mississippi Valley.
On a positive note, the heaviest rain will pass south and east of hard-hit flood areas of Oklahoma, Kansas, Iowa and northern and western Missouri. This may allow rivers and streams in the area to further recede.
As the corridor of torrential rain advances eastward, it will reach needy areas of the southeastern U.S. late this week and this weekend. The rainfall could provide relief from drought and abnormally dry conditions that have been building across the region. However, even in some of these eastern areas, too much rain could fall and may result in flooding.