September 24-30, 2003
Midwest Weekly Highlights - September 24-30, 2003
A Stormy Beginning to Autumn
The week of September 24-30 marked the start of autumn in the Midwest. Two active cold fronts moved through the region, bringing copious rain from Missouri to Ohio, while their parent low pressure centers rained on the northern Great Lakes area and southern Canada. Widespread totals of 1.5-2.5 inches of rain were reported from central and southern Illinois, through central and northern Indiana, into far southern Michigan and most of the northern half of Ohio (Figure 1). Within this region, heavier rain bands were formed, with some exceeding 5 inches of rain for the period. The Upper Peninsula of Michigan and far northeastern Wisconsin also received two or more inches of rain. Unfortunately, most of the drought areas in the Midwest were bypassed; less than 25% of normal precipitation fell in Minnesota, southwestern Wisconsin, Iowa, and northwestern Missouri (Figure 2). The cold frontal passages did bring progressively colder air, with the week starting near normal and plunging far below normal by the end. Temperatures were especially below normal in Minnesota and Iowa (Figure 3). Only far southern Michigan had any drought amelioration this week, while areas near the meeting point of Minnesota, Wisconsin, and Iowa continued to dry (Figure 4).
First Front
The first cold front entered the Midwest on the 24th and exited on the 25th. It produced significant band of precipitation in central Indiana and southern Michigan. The front was generally somewhat dry, but some convection in the warm sector ahead of the front organized into a strong mesoscale convective system in east-central Illinois on the evening of the 23rd and was still strong in Ohio the next morning (Figure 5, NWS). The rain was especially heavy early in the path of the storm, in Vermillion County, Illinois, next to the Indiana border (Figure 6, NWS). While this normally would have affected only a small number of farmers, this year the 50th Annual Farm Progress Show was being held at this location. Over 100,000 had attended the first day of an event planned for three days. However, the rains on already moist ground saturated the dirt parking areas, and the last two days of the event were cancelled.
Second Front
The second front entered the Midwest late on the 25th, just as the previous front was leaving to the east. This system was more powerful than the last, and also tapped Gulf moisture. On the 26th, warm frontal convection resulted in some rain before the main front arrived, with the issuance of some severe thunderstorm warnings near the junction of the fronts (Figure 7, Hydrometeorological Prediction Center). An upper air jet stream moved overhead, and a huge squall line developed along the length of the front, from Kansas to northern Illinois (Figure 8a and Figure 8b, College of DuPage). The junction between the warm and cold front developed a complex series of three thunderstorm clusters in central Illinois (Figure 9, NWS) before consolidating into one line over Indiana. Two confirmed tornadoes occurred along the front, a weak one in Logan County, Illinois, and an F-1 tornado in Hamilton County, Indiana. The latter caused significant structural damage to homes and farms and some crop loss, but no injuries. A lightning strike in Cohokia, Illinois, ignited a propane pipeline at a terminal along the Mississippi River. There were a total of about 90 severe wind and hail reports (Figure 10, Storm Prediction Center), although the damage was fairly light for a large area that was prognosticated to be in moderate risk for wind and hail (Figure 11, SPC).
Indiana received another large dose of rain with the second front, suffering widespread one inch totals punctuated by bands with 2-3 inches (Figure 12, NWS). Rivers started to rise above flood stage for the third time since the beginning of July, with the Wabash in Lafayette, Indiana, indicating a higher stage than after the Labor Day flood (Figure 13, USGS). Indianapolis set its all time record for September precipitation total, at 10.29 inches. This was also their tenth wettest of all months on record. Fortunately, serious flooding was not expected, as a cold dry high pressure system dropped into the area from Canada. While the western Corn Belt had an accelerated harvest due to the rapid drying of the grains and good field access, many fields in the Ohio Valley states were too wet to access, and some late crops were still susceptible to frost as a very cold morning marked the end of September.