Feb. 27 Update: The NWS reports that the "severe weather threat is diminishing." Our latest story updates are here. Our original story continues below.
A large storm system currently impacting the southwestern and central United States could potentially bring a wide array of threats to the Chicago area Monday morning, including flooding, gusty winds and even the possibility of an isolated tornado.
According to a hazardous weather outlook issued by the National Weather Service, the system is expected to start impacting Illinois and northwest Indiana late Sunday and into early Monday morning.
That system could dump an inch or more of rain on already-saturated ground and into already-elevated rivers, making the possibility of flooding a real concern for forecasters.
What’s more, the system could also generate thunderstorms, especially south of Interstate 80, and some of those storms could be strong-to-severe, according to forecast models.
Parts of Kankakee County in Illinois, as well as Newton and Jasper counties in Indiana, are at a "slight" risk of severe weather Monday, according to the Storm Prediction Center. LaSalle, Kendall, Grundy, and Will counties in Illinois, along with Lake, Porter and LaPorte counties in Indiana, are at a "marginal" risk of severe weather.
As a result, officials warn that a brief tornado could be possible in areas south of the interstate, with damaging winds in excess of 40-to-45 miles per hour also possible.
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No watches have currently been issued, but forecasters say those could be in the offing as the system approaches.
According to a hydrologic alert issued by the NWS, soil moisture is “above average” in both Illinois and Indiana, and as a result water runoff into area rivers could potentially cause flooding concerns, especially in lower-lying areas.
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Affected river basins include the Fox, Des Plaines, Rock and Kankakee rivers, according to NWS forecasters. Those rivers could rise to “near or above bankfull” if heavy enough rain falls in the area, according to forecasters.
The Iroquois River, which was experiencing minor flooding Saturday in a swath from Newton County in Indiana to the river’s confluence with Sugar Creek in Iroquois County, could see those water levels rise again because of heavy rainfall, which could flood agricultural areas near the river.
Again, no flood watches or warnings have been issued, but weather officials are urging residents to keep an eye out for alerts, especially those who live in low-lying areas near rivers.
The system is expected to arrive late on Sunday, with the heaviest rainfall expected to impact the area on Monday morning. That’s when thunderstorms could fire, especially in the far southern suburbs, and the highest likelihood of severe weather currently exists along, and south of, the Kankakee River Valley.
The rain will likely move out of the area by Monday afternoon, with most areas likely seeing an inch or more of rain.