By Dan DePodwin, Meteorologist
Mar 21, 2012; 1:05 PM ET
Over a half a foot of rain has already fallen in parts of Louisiana and more torrential downpours will lead to a dangerous situation in the Bayou State and others in the Lower Mississippi Valley today.The powerful storm that brought severe weather to the Plains earlier in the week has pushed into the Mississippi Valley. Heavy rain has been falling in parts of Louisiana and Arkansas since late on Tuesday and the deluges will continue today.
Rainfall totals through Wednesday afternoon included 15.89 inches 6 miles south-southwest of Leesville, La., 12.47 inches, 11.10 inches 5 miles west of Vinton, La., and 9.70 inches 4 miles northwest of Orange, La.
**Heavy rain and thunderstorms were crawling eastward across Mississippi this afternoon. While the greatest threat continues to be from flash flooding, a few of the storms can bring damaging wind gusts. Of these storms a small number can produce quick spin-up tornadoes. Some of the tornadoes may be shielded by rain and difficult to see as a result.**
**Confirmed Tornadoes From Wednesday: An EF1 tornado touched down near Lake Arthur, La. early Wednesday morning. The storm damaged between 20 and 30 homes. An EF1 touched down in Gueydan, La., damaging approximately 20 homes on Wednesday morning. An EF0 tornado struck about 1 mile west of Henry, La. The tornado blew the roof off of a barn, destroyed many outbuildings and snapped several trees.**
The prolonged period of very heavy rain is causing flooding problems as heavy thunderstorms remain over the same area for an extended period of time. This is known as "training effect."
A flow of moisture from the Gulf of Mexico is fueling the freight train of drenching storms. Due to the south-to-north orientation of the flow, the storms can only crawl to the east. As a result, the conveyor belt of heavy rain remain nearly stationary.
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AccuWeather.com meteorologist Bill Deger points out, "By Thursday, up to 8 inches could have filled some rain gauges, with flooding threatening to advance to some larger creeks and small rivers."
As the rain falls in sheets, visibility will be significantly reduced, hampering travel. Roadways will also become flooded in places. Never drive through flood water and slow down if driving in heavy rain to prevent hydroplaning.
Motorists driving along Interstates 10, 12, 20, 49 and 55 in Louisiana, in addition to I-30 and I-40 in Arkansas will have to deal with poor traveling conditions.
Residents of the Deep South will have to deal with up to an additional 6 inches of rain today and tonight before the storm system begins to weaken and shift north and east.
By Thursday and Friday, the heaviest downpours are expected to shift into the Tennessee and Ohio valleys, although rainfall amounts will be much less.
In addition to flooding rain, severe weather will also be a threat. Damaging winds and even an isolated tornado is possible today.
This amount of rainfall is unusual for the month of March, let alone in such a short time period. For example, the normal March rainfall for Shreveport, La., is 4.14 inches and they have received 4.43 inches from this storm alone!
The good news is that after this storm moves away from the region on Thursday, dry weather should prevail through the weekend and into at least early next week.
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