A low pressure system will drift into the region and stall, bringing the chance of heavy rains.
While overall rainfall amounts into the weekend may average in the 1 to 2 inch range, locally higher amounts will be possible.
The National Weather Service says be aware if you get a particularly strong storm, or repeat showers and storms over the same area, you may experience temporary, heavy downpours capable of producing flood issues.
The entire area is under a slight risk of rainfall exceeding flash flood guidance through Thursday night, and a marginal to slight risk exists Friday and Friday night as well.
Parts of southern Illinois are nearing the crest of the flooded Mississippi River this weekend.
Illinois State Police used the closed Cora floodgate near the Jackson-Randolph County as an example of why it's important to heed the warning signs to avoid danger.
Illinois State Police Safety Education Officer Bridget Rice.
"We urge you, follow the signs, follow the detours. Your life may depend on it."
This year's flood is officially the third worst in Chester's history and the National Weather Service's new crest prediction of 46.1 feet would make it the second highest, behind the all-time high of 49.74 feet in 1993.
Crests along the Mississippi River at Thebes and Cape Girardeau are expected to be in the top ten all-time for those locations.
The Illinois Department of Natural Resources is urging the public to stay off Illinois rivers.
IDNR spokesperson Rachel Torbert says it's not safe to be on the water during a major flood.
"We would just ask folks to stay off the water, especially if the river's in flood stage because it not only puts their safety at risk, but puts the safety of our first responders and law enforcement at risk as well."
She says that includes strong currents and debris.
"We're talking about branches and other things that may be along the river's edge there that could easily ensnare or trap someone. Those things that you can't see are the things that are most dangerous."
Torbert also warns residents to stay off levees, since many are critically unstable at this point.