Midwest Overview - August, 2006

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Hot Start, Cool End to August

Much of the Midwest experienced temperature near to slightly above normal during August, with one notable exception. Temperatures in all but extreme northern Missouri averaged 2°F to almost 5°F above normal during the month (Figure 1). This was largely the result of unusually persistent hot weather the first half of the month, when triple-digit temperatures were occurring on a regular basis.  Temperatures the first 15 days of the month were 5°F to 7°F above normal across most of Missouri, while only 1°F to 3°F above normal of the rest of the region (Figure 2). In contrast, temperatures the last 16 days of August ranged from 1.5°F below normal to 2.5°F above normal across Missouri (Figure 3). The first week of August was the warmest across the Midwest, with a number of record high minimum temperatures set during the first three days of the month as dewpoints remained in the 70s. The last week of the month brought much cooler weather with temperatures averaging  from 1°F to 2°F above normal in eastern Ohio and Kentucky to 5°F below normal in western Missouri.

Rainfall in August was near to well above normal across most of the Midwest (Figure 4). The northeastern periphery of the region was the driest, with rainfall less the 50 percent of normal in portions of northern Minnesota and northern Wisconsin, and 50 to 75 percent of normal in southern Michigan, much of Ohio, and eastern Kentucky. The abundant rainfall across the central portion of the region was due to active frontal boundaries that tended to stall out across the central Midwest. Some of the heaviest rain fell in the drought-stricken areas of Missouri, Iowa, and Minnesota. However, the rain was not always spread out over the month, and in some cases fell over the period of a day or two. The Kansas City, MO area received six to seven inches of rain on August 27, almost twice what would normally be expected for the entire month.

The presence of frontal systems in the Midwest provided the focus for severe weather this month, especially when interacting with periodic upper level troughs of low pressure. The largest concentration of severe weather during August was across the northern Midwest where the jet stream was active. Several tornadoes caused damage in Minnesota during the month, including an F3  twister which resulted in one fatality on August 24 in south-central Minnesota.  The same storms pummeled the same area with three to four inch hail causing extensive damage and some injuries.

 
Summer Weather

Despite some very hot and humid periods during the summer, average temperatures for the summer (June, July, August) were near to only slightly above normal (Figure 5). Northern Minnesota and northwestern Wisconsin were warmer with departures of 2°F to 3°F above normal.  June was a cooler than normal month across much of the Midwest. July was warmer than normal, especially over the northern Midwest. August temperatures were generally 1°F either side of normal.  Precipitation for the three month period was 75 to 100 percent of normal south of a line from Sioux City, IA to Saginaw, MI (Figure 6). North of that line precipitation dropped to as low as 50 percent of normal in northern Minnesota, which remained in Extreme Drought at the end of August. Even in areas that received normal rainfall, the rain was not evenly distributed across the summer and dry, hot weather caused serious problems for agriculture especially in Missouri, Iowa, and Minnesota.