An elevated threat of flash flooding is expected this weekend across the southern Great Lakes, with heavy rainfall affecting areas already soaked this week including Chicago into parts of Indiana and Ohio.

Happening now

The map below shows where rain is falling right now, along with any flash flood warnings in the green polygons.

The heaviest rain through early Saturday is expected in parts of the upper Midwest, from Minnesota and Iowa into Wisconsin and northern Illinois.

Local flash flooding is possible in cities such as Minneapolis-St. Paul, Madison, Milwaukee and at least parts of Chicagoland.

Day by day forecast

On Saturday, the heaviest rain shifts a bit to the south and spreads east.

Two rounds of heavy rain are possible, one in the morning and another in the evening, across portions of southern Wisconsin and northern Illinois. They could linger over those areas, including Chicago and Milwaukee, for several hours with high rainfall rates.

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Flooding is likely in the area marked in red on the map below.

On Sunday, the heavy rain threat may linger from northern Illinois through northern Indiana and western Ohio, while also spreading into parts of the Northeast.

How much more rain? 

Several inches of additional rain are likely in the darker green and yellow contours in the map below.

The biggest concern this weekend is the corridor from eastern Iowa into northern Illinois, northern Indiana and western Ohio, where flooding rain fell earlier this week. Additional heavy rain is likely to lead to additional flash flooding and perhaps some river flooding once again.

Why the flooding?

The rainfall this week is due to a slow-moving frontal boundary that's drifting across the Midwest and Central Plains. This front is clashing with the outer rim of a stubborn heat dome over the South, allowing it to generate some heavy rain and storms.

This front has stalled out since the heat dome is blocking its path, resulting in days of flooding over the same areas.

The heat dome will stay put through the weekend, forcing rain and storms to track around its outer edge. The graphic below shows the area that has the greatest chance of flooding for the next several days.

(MORE: Why the Midwest flooding kept hitting the same areas)