August 25-31, 2003
Midwest Weekly Highlights - August 25-31, 2003
Change in the Midwest
The last week of August marked a tremendous change in surface conditions in the southern half of the region, from overly warm and dry to cool and very wet. While some heavy rain occurred as early as the 28th and 29th, a plume of deep moisture streamed northward from the Gulf of Mexico after the landfall of Tropical Storm Grace and overran a stationary front draped across the region. This front, arcing from southwestern Missouri into central Illinois and then on to Ohio and beyond, was the focal point for general rains of 2-4 inches (Figure 1), with some narrow band receiving up to 10 inches of rain through September 1st. Precipitation totals for the week reached 200-500% of normal (Figure 2) in the five state region including most of Missouri, Illinois, Indiana, Ohio, and Kentucky. Temperatures were still 2-5°F warmer than normal for the week in the southern two-thirds of the Midwest (Figure 3), but conditions cooled considerably north of the stationary front and in the cloudy zone of precipitation near the front. Midwest drought conditions reached the lowest point of the year in the August 26 Drought Monitor (Figure 4, National Drought Mitigation Center), but there should be some improvement registered where the rain fell. Unfortunately, most of the rain steered clear of Nebraska, Iowa, and some other dry north-central portions of the Midwest. Even where the rain landed to the benefit of late planted or more slowly maturing crops, there were places where damage was irreversible at this time of the growing season.
Second Heat Maximum and the Peak of Drought Extent
The month of August was very dry through the 28th, with 3-4 inch deficits occurring in less than 30 days in parts of Iowa, and only small zones of the southern and eastern Midwest receiving above normal precipitation (Figure 5). The combination of extreme dryness and hot temperatures took quite a bit of quality and yield off western and central Midwest soybeans and corn. In Iowa, corn rated as good/excellent was down to 36% by August 31, 10% less than the previous week, and soybeans rated good/excellent diminished to 30%, a 13% reduction. Row crops in Iowa, Missouri, Minnesota, and Wisconsin have been deeply impacted by drought, with corn kernel weights much below last year and soybean pods filling with just a couple lightweight beans. Only crops that were planted late would be able to recover from the effects of the drought and intense heat over the last 6 weeks, even if rain did arrive. Livestock operations were also hard hit by the lack of water in farm ponds, the intense heat, and pastures turning tan and drying up.
Heat wave conditions returned in the western Midwest as the period began with Kansas City having another three day run with the maximum temperature above 100°F from the 24th to the 26th. Temperatures above 100°F were most common on the 25th (Figure 6), while a number of records were set in Iowa and Illinois on the 26th (Figure 7), including at Dubuque and Burlington, IA, and Moline and Rockford, IL. An additional person died of heat related causes in the Kansas City area., and the beginning of the school year was disrupted from Kansas to Ohio by extreme heat forcing school systems to send students home early or cancel classes outright.
Flooding Rains over a Five State Area
Early in the week, there were several outbreaks of convection in the far northern and eastern Midwest, as upper level disturbances went around a ridge that was keeping the rest of the region dry. The surface high pressure dominating the region slipped off to the east and allowed a return flow of moisture from the Gulf of Mexico to reach the central Midwest as a cold front approached from the west. Substantial rains occurred ahead of the frontal boundary on the 28th with a series of thunderstorm clusters arcing from Kansas (Figure 8a, College of DuPage) to Wisconsin (Figure 8b, COD). The northern part of the front lost momentum, and the southern part of the front became stationary, with clusters of thunderstorms continuing eastward through central Illinois and Indiana later on the 28th and early on the 29th (Figure 9, NWS). The accumulation of precipitation was substantial in Kansas and western Missouri (Figure 10a, NWS), eastern Missouri (Figure 10b, NWS), central Illinois (Figure 10c, NWS), and central Indiana (Figure 10d, NWS) by the evening of the 29th. Some street flooding occurred in urban areas, but the agricultural soils largely absorbed the first dose of moisture.
In conjunction with the approach of Tropical Storm Grace to the Texas coast, a deep plume of moisture from the Gulf of Mexico flowed northward towards the stationary boundary extending from Kansas to Ohio on August 30. Very heavy precipitation developed over Kansas and Missouri first, and then spread eastward across the central Midwest, organized by the stationary front. Flood watches spread from Kansas to Indiana on the 31st (Figure 11, Storm Prediction Center). Heavy rain was falling over a wide band across northern Missouri (Figure 12a, NWS), Illinois (Figure 12b, NWS), and Indiana (Figure 12c, NWS). However, it was not until the precipitation totals for the period from August 28 to the morning of September1 were accumulated that the magnitude of the event is apparent. Precipitation accumulation in parts of Kansas and western Missouri exceeded 10 inches, both in radar estimates (Figure 13a, NWS) and by surface observations. Kansas City, MO, Watts Mills district received 10.52 inches of rain, Raytown received 10.12 inches, and the Downtown station received 8.73 inches from August 28 to 7 AM on September 1. One person drowned in the Overland Park suburb when he was swept away crossing a creek. However, the degree of flooding near Kansas City was minimized by the high degree to which the precipitation was absorbed by the drought afflicted soils. The same could not be said about sections of Kansas to the southwest, near Emporia. In this area, 7 cars were swept off of I-35 in a flash flood that reached depths of over 5 feet and moved 10,000 lb concrete barriers, in addition to the cars. Four children and their mother died in one of the vehicles, and a person aiding the occupants of another car was swept to his death.
Further east, tremendous precipitation totals can be found embedded within widespread 2 to 4 inch radar precipitation estimates for northeastern Missouri (Figure 13b, NWS), central Illinois (Figure 13c, NWS), central Indiana (Figure 13d, NWS), and west-central Missouri (Figure 13e, NWS). In fact, the totals for Illinois, Indiana, Ohio, and Kentucky were incomplete at that hour, as rain continued well into the next week in the eastern and southern Midwest. The plume of moisture from the gulf was evident in a water vapor image from the morning of September 1, including the rotation over the Texas/Oklahoma border associated with the remnants of TS Grace (Figure 14, COD). Flood watches and warnings spread all across the Midwest into the Northeast (Figure 15, SPC). While urban flooding and some minor river flooding occurred in the dry stretches of Missouri and Illinois, major flash flooding and river flooding was in progress at the end of this reporting period in Indiana, Ohio, and Kentucky (Figure 16, USGS). Further reports summarizing the flood impacts in these areas will be described in the next weekly summary.
Scattered Severe Storms
Prior to the flooding rains late in the period, a well-organized bow echo of thunderstorms (Figure 17, NWS) moved through Indiana and Ohio and into the east on the August 26, leaving a trail of severe wind event reports (Figure 18, SPC). [The extension of the severe wind event reports into the Washington, DC, area was due to another bow echo formed east of the Midwest region, and not the original Midwestern bow echo.] About 70,000 customers lost power in northern Indiana at the start of bow echo life cycle, mostly due to straight line winds exceeding 80 mph. More than half of these customers were without power for more than 12 hours due to the widespread damage to trees and power lines in the affected area, and 5000 were without power for more than 3 days. The wind damage cut a similar swath through Ohio and parts of West Virginia. In Ohio, some intense precipitation events were also noted with these storms, including localized totals of 5 inches in eastern Ohio, and a burst of 1.40 inches in 40 minutes in Dayton, OH. A few small embedded tornadoes familiar to bow-echo environments were also noted in northern Indiana and Ohio, touching down briefly in both cases and causing extensive damage to a few buildings. Several small tornadoes with brief touchdowns were also noted in the southern portions of the rain shield on August 31, but caused little damage (Figure 19, SPC).