May 11-21, 2002: Major Flooding in Missouri, Illinois, and Indiana.

Major flooding visited the Midwest during the period May 11 to 21. The Mississippi and Ohio Rivers reached more than 10 feet above flood stage in places, and many regional rivers such as the Illinois in Illinois, the White in Indiana, and the Meramec in Missouri reached even higher levels above flood stage. A minimum of 3 inches of rain fell throughout Missouri, Illinois, Indiana, and western Kentucky, and more than 6 inches fell in parts of southeastern Missouri and southernmost Illinois (Figure 12). For the eleven day period, precipitation exceeded 200% of normal over most of the southern half of the Midwest, and exceeded 300% of normal in the wetter areas of Missouri and Illinois (Figure 13). For the month of May, at least 12 stations in Illinois and 25 in Missouri received more than 10 inches of rain through the 21st. The largest observation was made at Fredricton in southeast Missouri, where 16.03 inches of rain were received between May 1 and 21. Due to the rainy and overcast conditions during the period, temperatures were far below normal, with most of the central and northern Midwest more than 10°F below normal (Figure 14). Drought in all its forms has now departed Midwest (Figure 15), only to be replaced by an overabundance of rain.

The heaviest rain fell in the first half of the period in the southern Midwest. From May 12-13, more than 5 inches of rain fell in some places in Missouri, Illinois, and southern Indiana (Figure 16a and Figure 16b, CPC). While the return interval for a 2-day, 5-inch rain event is about 10 years at an individual location, the widespread nature of an event of this magnitude was even more unusual. Adjacent areas received up to 2-4 inches of rain. Several waves of convection trained along a very slowly moving cold front. Some severe weather reports were made, but most of the warnings issued were related to flash flooding on already saturated ground and increased river stages on top of previous flooding conditions. After a few calm days, the second major rain producing system of the period passed through the area on May 17-18, contributing several more inches of rain to the southern third of the Midwest and lesser amounts to the central Midwest (Figure 17a and Figure 17b, CPC). Only on the 18th did a strong cold front pass, and record-setting cold but dry air dominated to the end of the 21st.

The flooding and ground saturating rain in the Missouri, Illinois, and Indiana greatly impacted agriculture. Tens of thousands of acres were inundated by streams and rivers, and many areas of low topographical relief also filled with water. Corn planting was completed in Missouri before the flooding, but is 3-4 weeks behind normal pace in Illinois and Indiana. Many fields in the southern parts of each of these states will have to be replanted after some 7-10 days of drying. In addition, temperatures were exceptionally cold, with more than 300 temperature related records set in the U.S. between May 18 and 21. On the morning of May 21, Chicago experienced its latest sub-freezing temperature in recorded history, reaching 31°F just a month before the summer solstice (Figure 18). Even in areas not gravely impacted by excess moisture, the cold temperatures have been slowing crop progress and harming fruit trees, especially the cherry crop in Michigan. Field cropping decisions in flooded areas are almost at the critical dates in which crop insurance values decline for each day of delay in planting. Some farmers have switched from corn to soybeans. It remains to be seen what the influence of the wet spring will be on the Corn Belt.