Midwest Overview - August 2009
Another Cool Month
The unseasonably cool weather of July continued into the month of August. Temperatures in August were near normal in eastern Ohio, dropping to 3°F below normal in western portions of the region (Figure 1). The 10-day period from August 8-17 was the only substantially warm period during the month, with temperatures averaging near normal across Missouri to 5°F above normal in the northern portions of the Midwest (Figure 2). Average daily low temperatures during the month were near to slightly above normal in eastern Ohio decreasing to 2°F to 3°F west of the Mississippi River. The cool weather was dramatically seen in the average daily maximum temperatures, which were as much as 6°F below normal in western portions of the region (Figure 3). Based on preliminary August temperature data, this was the 21st coolest August on record for the Midwest. There were several monthly temperature records set as Canadian high pressure settled over the area at the end of the month.
Rain Targets Central Midwest
Frontal systems repeatedly moved out of the Northern Plains and into the Midwest in August, providing a focus for showers and thunderstorms. These systems frequently slowed or stalled across the central Midwest, resulting in an axis of heavy rain from northwestern Missouri through southwestern Iowa into northern Illinois (Figure 4). Rainfall in southeastern Iowa exceeded 13 inches for the month at some locations. Clutier, IA (Tama County) reported 13.65 inches, Cedar Rapids (Linn County) 13.05 inches, and there were a number of other reports of more than 10 inches for August. Monthly rainfall was from 175 percent to almost 300 percent of normal in this band (Figure 5). Many locations set record daily precipitation amounts for the month of August. Outside of this band, rainfall in August was spotty, with some areas receiving normal to above normal rainfall and surrounding areas less than 50 percent of normal. Significant rain fell in central Minnesota and northwestern Wisconsin toward the end of the month, providing some improvement in the drought situation there. However, at the end of the month drought was still classified as severe in northwestern Wisconsin and the southern Michigan U. P.
While heavy rain was more frequent in the central Midwest, the most damaging heavy rain occurred on August 4 in the Ohio Valley. Up to seven inches of rain fell in an hour in parts of the Louisville, KY metro area (Jefferson County), causing millions of dollars of damage to notable landmarks such as Churchill Downs racetrack, the University of Louisville campus, and the downtown public library. Hundreds of homes were damaged by the resulting floodwaters and more than 20,000 homes lost power. While hundreds of people were rescued by various emergency agencies, remarkably there were no fatalities or injuries from the flooding. Heavy rain that ranged from two to four inches fell in several other counties along the Ohio River as well as in more isolated thunderstorms in Butler County and near Paducah, KY (McCracken County) on that day.
All nine Midwestern states experienced severe weather during August (Figure 6). The majority of the severe reports this month came on August 4 and on August 19-20. The storms on August 19 included 30 tornado reports in seven Midwestern states, including at least one twister that touched down in downtown Minneapolis, MN (Hennepin County).
Temperatures for the summer season (June-August) were near to below normal across the Midwest. Temperature departures ranged from near normal in eastern Ohio to 4°F below normal in western and northeastern Minnesota (Figure 7). Modified growing degree days (MGDD) for the Midwest since May 1 were below normal for the entire region at the end of August (Figure 8). MGDD departures ranged from 50 MGDD below normal in southern Kentucky to 400-450 MGDD below normal in portions of Minnesota. Late planting due to a wet spring and the cool summer weather contributed to slower than normal development of corn and soybeans in portions of the Midwest. At the end of August corn crop development was from three to four weeks behind in Illinois, three weeks behind in Kentucky, two weeks behind in Indiana, one to two weeks behind in Minnesota, and a week or more in Missouri and Iowa. Soybeans are on a normal pace in Iowa, but a week behind in Illinois, Indiana, and Missouri.
June was the only month where temperatures averaged above normal somewhere in the Midwest. Temperatures across the southern third of the Midwest in June were 1°F to 3°F above normal, while they ranged from 1°F to 3°F below normal across the northern third of the region. July was the coldest July on record across the Midwest, with temperatures 2°F below normal in eastern Ohio to as much as 6°F below normal in eastern Iowa. There were fewer than 20 record highs observed while more than 1800 record lows were recorded in July. August was also colder than normal across the entire region, with temperatures ranging from near normal in eastern Ohio to 4°F in portions of Minnesota.
Precipitation was normal to above normal across most of the region, with the greatest positive departures from southeastern Iowa across northern Missouri, and in the Ohio Valley (Figure 9). Rainfall was less than 75 percent of normal from the northern half of Wisconsin into central Minnesota, where drought has persisted since spring. Heavy rain the last ten days of August slightly improved conditions in that area, but drought still persisted at the end of the month.
For more details on weather and climate events during August 2009, click on the individual weekly report links on the upper right.