July 2011
Midwest Overview - July 2011
A Summer Sauna
Hot and humid weather held sway across the Midwest for most of the month of July as the result of a persistent upper level ridge over the central United States (Figure 1). Average daily temperatures ranged from 3°F to 6°F above normal during the month, with the greatest departures found in southwestern and western Missouri (Figure 2). For all nine Midwestern states this July ranks in the top seven warmest Julys, based on preliminary data. The hot weather was accompanied by very humid air, with dew points frequently remaining in the 70s and even reaching the low 80s in some locations. At Moorhead, MN (Clay County), a dew point of 88°F was measured from 7:00 p.m. to 9:00 p.m. on July 19th. That is a new record for the state of Minnesota. The previous dew point temperature record was 86° F set at Pipestone (Pipestone County) and St. James (Watonwan County) on July 23, 2005. The combination of high temperatures and dew points produced heat indices frequently in excess of 110°F. The peak of the heat wave occurred during the third week of July.
Daily average maximum temperatures ranged from as much as 8°F above normal in southwestern Missouri to near normal in Kentucky (Figure 3). Maximum temperatures in an area encompassing eastern Indiana into western Ohio were 5°F to 6°F above normal. The humid air mass prevented overnight temperatures from falling enough to provide relief from the oppressive conditions. Daily average minimum temperatures were generally 4°F to 6°F above normal, except south of the Ohio River and in far northern Minnesota (Figure 4). It was the high minimum temperatures that helped push rankings for this July into the top seven for the Midwestern states. Preliminary data show that 1,581 record high minimum temperatures were tied or set in the Midwest during July, with 920 occurring in the five-day period from July 18-23. In contrast, there were only 528 record high temperatures tied or set during the entire month.
Missouri Bakes
Southwestern Missouri experienced almost unrelenting heat, with only periodic breaks in the weather. Preliminary numbers indicate Missouri experienced its hottest month in more than 30 years. The average statewide temperature for the month was 83°F, slightly over 5°F above normal, and the hottest month since July 1980. It was also the 6th hottest July on record and will go down as the 8th or 9th hottest month of all time when final numbers are tallied.
Monthly temperatures averaged 81°F to 82°F across northern sections and the eastern Ozarks region, 82°F to 84°F over central, east central and southeastern sections and 84°F to 87°F in west central and southwestern Missouri. Springfield and Joplin, MO experienced 8 and 19 days, respectively, of triple-digit heat and both recorded their third hottest July on record. The highest temperature for the month was reported in two southwestern locations on separate days. The communities of Protem (Taney County) and Ava (Douglas County) reported 107°F on July 11 and July 27, respectively.
Hot temperatures and high humidity combined to produce very uncomfortable and life threatening conditions during the month. According to the Missouri Department of Health and Senior Services, there were 11 heat related fatalities between May 1 and July 31 and another 24 deaths were likely heat related. The majority of deaths occurred during July and in the St. Louis metropolitan area. More than 1,300 heat related visits to emergency rooms were documented statewide for the period.
Where It Rained, It Poured
A large portion of the Midwest saw less than normal rainfall in July. The most persistent and heaviest rains fell on the periphery of the large upper ridge, where a boundary between the hot humid air south and slight cooler air to the north often stalled out. Rainfall was 150 to more than 200 percent of normal from west-central Minnesota east-southeast across southern Lower Michigan (Figure 5). Rainfall was also well above normal across southern Illinois. There were a number of significant heavy rain events during the month in these areas, and record daily precipitation amounts were set in several locations the last two weeks of July. More than seven inches of rain fell in the Chicago area July 22-23, and more than four inches fell in northeastern Ohio, causing extensive flash flooding in both areas. On July 28th more than 15 inches of rain accumulated in a relatively small portion extreme eastern Iowa and northwestern Illinois, causing extensive damages from flash floods and one fatality. Dubuque, IA (Dubuque County) received 16.01 inches of rain in July, but that total was swollen by a record 24-hour rainfall of 10.62 inches on the night of July 27th. Their July total was the highest for any month at that location among 158 years of records (old record 15.46 inches in September 1965).
Severe weather occurred in all nine states in July, but was concentrated from Minnesota through Wisconsin, northern Illinois, and eastward into northern Ohio (Figure 6). Most of the reports were for severe thunderstorm winds. The most significant event was a long-lived derecho that developed in Nebraska on July 10th and swept across central Iowa, southern Wisconsin, northern Illinois and Indiana, and much of Ohio late on the 10th and July 11th. Measured wind gusts to 80 miles per hour were reported, and wind were estimated as high as 110 miles per hour near Dysart, IA (Tama County).
Missouri River Flooding
Minor to major flooding continued along the entire length of the Missouri River in Iowa and Missouri in July, with a gradual decrease during the month especially in the eastern portions of the river basin. Major flooding was still in progress at St. Joseph, MO (Atchison County) at the end of July, but was expected to fall below major flood stage in early August.
For more details on weather and climate events during July 2011, click on the individual weekly report links on the upper right.
The Iowa State Climate Office, the Missouri State Climate Office, and the Minnesota State Climate Office also contributed to this report.
-SDH-