July 1-10, 2004
Midwest Weekly Highlights - July 1-10, 2004
July Starts With a Bang
Nature provided an active weather pattern during the period of July 1 and 10, in some cases replacing cancelled fireworks displays with its own natural fireworks. Unlike the ending half of June, the first ten days of July were wet in most of the Midwest except for the eastern Ohio Valley. The Minnesota-Iowa border region and southwestern Missouri received 3-6 inches of rain over widespread areas, with some individual locations exceeding 7 inches (Figure 1). Much of Illinois, Iowa, Missouri, Michigan, and southern Wisconsin received 150-300% of normal precipitation for the period (Figure 2). Temperatures were generally colder than normal, except in the Ohio Valley (Figure 3). Most of the northwestern half of the region was greater than 4°F below normal, with some locations in the wet Upper Peninsula of Michigan more than 8°F below normal. A number of record low maximum temperatures and a few record minimum temperatures were set at mid-period, but temperatures began warming considerably at the end of the period. Some rain fell in the dry area of northern Minnesota, but at mid-period, insufficient rain had fallen to prevent and expansion of the abnormally dry area and re-establishment of moderate drought status in central northern Minnesota (Figure 4, National Drought Mitigation Center). Finally, Iowa recorded its first death from West Nile Virus in 2004 in the southwestern corner of the state.
A Stormy 4th, and 3rd, and 5th, and 6th ....
The familiar circulation pattern of May and early June reestablished itself over the Midwest early in the period, with a quasi-stationary boundary moving north and south as surface lows and upper level waves passed through. A low pressure center started moving through the area on July 3 and July 4 (Figure 5, College of DuPage), triggering heavy rain in the northern Midwest and parts of Illinois and Indiana, including the Chicago metro area (Figure 6, COD). The worst severe weather, however, occurred on July 5, hitting the St Louis area with two separate clusters of thunderstorms during a single day. Storms in the morning (Figure 7, NOAA Radar Operations Center Archive) swept through St. Louis around 8:30 AM, causing extensive damage with 60-70 mph winds and some hail. These storms developed into a long-lived windstorm that swept through southern Illinois, southern Indiana and Kentucky leaving more than 100 severe wind reports in their wake (Figure 8, Storm Prediction Center). About 12 hours later, another cluster of storms (Figure 9, NOAA ROCA) returned to St. Louis with winds gusting past 70 mph, leaving behind more damage and severe wind reports there although weakening as it passed through the Ohio Valley. At its worst, more than 178,000 were without power in the St. Louis area, and about 12,000 were still without power two days later.
Further to the north, near the low pressure center, a small area of astounding precipitation
occurred in northeastern Iowa (Figure 10, NWS). In Fayette County, more than 7 inches of rain
fell in total; about 6 inches of this fell in three hours, which is 1.5 inches more than a 100-year
storm for this area. Severe flash flooding wiped out a variety of bridges in the drainage basins of
the Turkey and Volga Rivers. The Turkey River in Garber, IA, rose 13 feet in less than half a
day (Figure 11, US Geological Survey), and smaller streams were even more flashy. Moderate
flooding also occurred along some of the larger rivers and streams in the region, especially the
Cedar River. Considerable precipitation also accumulated in the multiple storm events through
Missouri and Illinois between July 3-6 (Figure 12, NWS). Agricultural interests in much of the
Midwest were concerned about the effects of this weather on the corn and soybean crops.
Cool Weather After Cold Frontal Passage
The temperatures on July 7 and 8 were very cold for the time of year. Record low minimum
temperatures were tied at Kansas City, MO, on the 7th and exceeded on the 8th at Dubuque, IA.
The daytime temperature maxima on the 7th, however, were very much more unusual, with
almost all of Minnesota, Wisconsin and Michigan remaining below 70°F for the daily maximum (Figure 13). On the 7th, record low maximum temperatures were set or tied at four locations in
Iowa, seven locations in Wisconsin, and at Marquette, MI, which reached a high of only 51°F.
Three more locations in Michigan set new daily records for lowest maximum temperatures on the
8th, but by the end of the day, a strong warm front return flow was taking place in the western
Midwest, leading to another bout of heavy rain and severe weather at the end of the period. The
quest for Kansas City to reach its latest date for a 90°F maximum temperature ended with the
period; the 10th was the last sub-90°F day, setting the second place mark.
Heavy Rains Around the Midwest, Drought Relief in Northern Minnesota
On July 8, a return flow of moist, humid air lifted over the cooler than normal air in the western Midwest, leading to widespread convection. Small but intense cells extended into southwestern Missouri from a larger system in Arkansas, but left enough precipitation to lead to flash flooding and a drowning death due to a car being swept off a road in Howell County, MO (Figure 14, NWS). Even though there was no surface low, sufficient upper air support was available to bring about organized convection in southern Iowa, and a small mesoscale convective system moved eastward across central Illinois and Indiana. By the morning of the 9th, a large mass of convective rain covered most of Iowa (Figure 15, NWS). Heavy rain totals were found from western Iowa (Figure 16, NWS) through eastern Iowa (Figure 17, NWS), and into Illinois and eastern Indiana (Figure 18, NWS). The evening of the 9th had another cluster of storms traveling through central Illinois (Figure 19, NWS), causing rain totals in eastern Illinois and central Indiana to reach 3-6 inches for the July 7-10 period. More general rain fell in the warm sector thunderstorms widely distributed through the southern Midwest on the 10th (Figure 20, COD).
Late on the 10th, a very heavy rain event commenced in the Dakotas and spread eastward into northern Minnesota. By the morning of the 11th, widespread rain totals of 2-3 inches were found along the Minnesota border (Figure 21, NWS). This rain, combined with expected rain in the next period, will probably result in a reduction of drought status in this area.