Flood Threat from Texas and Louisiana to the Ohio Valley to Last Into Early Next Week

Tom Moore
Published: August 12,2016
The threat of flash flooding, and eventually river flooding, will become more widespread from Texas and Louisiana to the Ohio Valley and parts of the Great Lakes in the coming days.
Already Friday morning, flash flooding has become serious in parts of Louisiana and Mississippi. Greensburg, Louisiana, was largely cut off by flooding, with water entering a hospital and nursing home. Some areas picked up over 10 inches of rain since late Thursday night.
(LATEST NEWS: Flash Flood Emergency in Louisiana)

Current Radar, Watches and Warnings.

The threat isn't just in the Deep South, though.
Flood watches have been posted in parts of southeast New Mexico and West Texas, the mid-Mississippi Valley and Great Lakes.

Current Flash Flood Alerts

There are actually two features that will be producing significant rainfall.
One is an area of low pressure that has produced some heavy rain and flooding to the Gulf Coast region this week. The other is a cold front that has been moving southeastward from the upper Midwest to the Plains. That system produced flooding over parts of the upper Midwest Thursday morning.
(MORE: Flash Flooding in Wisconsin, Minnesota Leads to Washed Out Roads, Water Rescues)

Heavy Rain/Flood Threat Forecast

Friday
The two weather systems will remain separate, so there will be a couple of areas that could see heavy rain and localized flooding. One such area stretches from southern Mississippi back to Louisiana, where a general area of 3 to 5 inches of rain is expected to fall.
Parts of southeastern Louisiana could see anywhere from 5 to 8 inches of rain, with locally higher amounts. Localized flooding is likely in these areas.
Rainfall totals of 1 to 3 inches, with locally higher amounts, could fall from Michigan, down through Wisconsin, to parts of Illinois and Missouri. Localized flooding could also occur in these areas.
Cities: Gulfport, Mississippi | New Orleans | Monroe, Louisiana | Chicago
Weekend
The two aforementioned weather systems will then join forces. Moisture from the Lower Mississippi Valley system will expand westward into northeastern Texas as the low-pressure system fades away. Moisture will then be pulled up ahead of the stalling front, and it will extend from eastern Texas all the way up to the Ohio Valley.
Showers and thunderstorms are likely to produce a general area of 1 to 3 inches of rainfall near the front.
From central Texas Arkansas to Ohio, 3 to 5 inches of rain is expected, with locally higher amounts. These areas should watch out for localized flooding.
Cities: Austin, Texas | Branson, Missouri | Carbondale, Illinois | Evansville, Indiana | Columbus, Ohio

Rainfall Forecast Through Wednesday

Next Week
The situation becomes a bit more uncertain because there are a number of factors that could determine how much rain falls and where flooding could occur. If the front remains in place, there could be very high rainfall totals and more widespread flooding.
Some model guidance indicates that the high-pressure ridge could weaken a bit and allow the front to sag southeastward. If this occurs, it could allow rainfall to spread out. Generally, we are still looking for significant rain to fall from eastern Texas through the mid-Mississippi Valley and into the Ohio Valley.
We will also be on the lookout for localized flooding. This general pattern is likely to remain at least through the middle of the week.
Cities: Little Rock | Memphis | Louisville | Cincinnati | Pittsburgh

Setup For Long-Term Heavy Rain 

Ingredients for Heavy Rain

The atmosphere can often become sluggish during the month of August as high-pressure ridges build; they can act as a blocking mechanism to storm systems that attempt to advance. The upcoming situation is a prime example. The weather systems involved with the current situation contain high amounts of moisture, which is why we're concerned about widespread heavy rain.
Heading into the weekend, a ridge of high pressure aloft (bulge in the jet stream) will expand westward from the East Coast. Meanwhile, a trough of low pressure (dip in the jet stream) will move southeast from the upper Midwest to the Great Lakes. This trough will weaken as it moves toward the blocking ridge, while the surface front stalls.
Therefore, we have three factors that will combine to create a heavy rain and flooding threat over a large area.
1. Plenty of moisture in the atmosphere from our two merging weather systems.
2. An upper-level "blocking" pattern that will hold for several days.
3. A stalled frontal boundary from Texas to the Great Lakes that will hold moisture in place, enhancing shower and thunderstorm activity.

Weekend Upper-Level Pattern

Please use extra caution due to the possibility of heavy rain and flooding if you live in any of these areas.
(MAPS: Weekly Planner)
MORE: Flooding in Ellicott City, Maryland