Flooding Possible During Multi-Day Heavy Rain Event From Western Gulf to Great Lakes

Tom Moore
Published: August 11,2016
A multi-day heavy rain event, with the possibility of localized flash flooding, is expected to sweep through an area from the western Gulf of Mexico region through the lower Midwest and into the Great Lakes in the coming days.
There are actually two features that will be producing significant rainfall during the late-week period.
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)

Current Radar, Watches and Warnings.

Heavy Rain/Flood Threat Forecast

Through 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 the Upper Peninsula of Michigan, down through Wisconsin, to parts of Iowa and Illinois. Localized flooding could also occur in these areas.
Cities: Gulfport, Mississippi | New Orleans | Monroe, Louisiana | Madison, Wisconsin | Chicago
Weekend
The two aforementioned weather systems will then join forces. Moisture from the western Gulf system will expand westward into northeastern Texas as the low-pressure system fades away. Moisture, associated with the low, will be pulled up ahead of the stalling cold front, and it will extend from eastern Texas all the way up to the eastern Great Lakes.
Showers and thunderstorms are likely to produce a general area of 1 to 3 inches of rainfall ahead of the front.
From northern Arkansas to southern Illinois, 3 to 5 inches of rain is expected, with locally higher amounts, from showers and thunderstorms. These areas should watch out for localized flooding.
Cities: Dallas | 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