From the National Weather Service in St. Louis
A flash flood watch has been issued for areas along and south of a Columbia, Missouri to Lincoln, IL line this evening into Sunday evening. Several rounds of thunderstorms with heavy rainfall are forecast across the area. Rainfall totals of 3 to 5 inches expected with locally higher amounts possible If this amount of rainfall is observed over already saturated ground, flooding of low lying areas will be likely. Those who live near creeks, rivers and streams should prepare for this heavy rainfall and the potential of flash flooding this weekend. Also, there is the potential of moderate to major flooding in river basins mostly to the south and east of St. Louis by early next week.