The Mississippi Valley could see historic rain and floods this week, with a rare level 4 of 4 high risk of flooding rainfall in effect Thursday for parts of Missouri, Arkansas, Tennessee, Kentucky and Illinois, according to the Weather Prediction Center.

“Extensive, rare, and at times catastrophic, flash flooding is likely… flash flood water levels may reach areas that rarely or have never flooded before,” forecasters at the National Weather Service in Little Rock, Arkansas, said.

It’s hard to overstate just how significant level 4 of 4, high risk flooding events are. They are issued on fewer than 4% of days per year on average, but are responsible for more than 80% of all flood-related damage and 40% of all flood-related deaths, research from the WPC shows.

Forecasters predict storms will work over the same areas repeatedly and could drop 2 to 6 inches of rain each day –– especially from Arkansas to Indiana.

By Saturday, areas caught repeatedly under the heaviest storms could end up with more than 15 inches of rain. The corridor where Arkansas, Missouri, Illinois, Kentucky and Tennessee meet are the most likely place for these extreme totals.